Main restoration working

Minor changes that speedup the large stress test.
Also now uses a stop token for a more productive shutdown. No need to wait for expensive GC runs.

.github/workflows/diff.yaml

@@ -96,7 +96,7 @@ jobs:
 
       - name: Python code analysis
         run: |
-          CHANGED_FILES=$(git diff -U0 ${{ env.BASE_BRANCH }}... --name-only)
+          CHANGED_FILES=$(git diff -U0 ${{ env.BASE_BRANCH }}... --name-only --diff-filter=d)
           for file in ${CHANGED_FILES}; do
             echo ${file}
             if [[ ${file} == *.py ]]; then
@@ -337,6 +337,116 @@ jobs:
             # multiple paths could be defined
             build/logs
 
+  experimental_build_ha:
+    name: "High availability build"
+    runs-on: [self-hosted, Linux, X64, Diff]
+    env:
+      THREADS: 24
+      MEMGRAPH_ENTERPRISE_LICENSE: ${{ secrets.MEMGRAPH_ENTERPRISE_LICENSE }}
+      MEMGRAPH_ORGANIZATION_NAME: ${{ secrets.MEMGRAPH_ORGANIZATION_NAME }}
+
+    steps:
+      - name: Set up repository
+        uses: actions/checkout@v3
+        with:
+          # Number of commits to fetch. `0` indicates all history for all
+          # branches and tags. (default: 1)
+          fetch-depth: 0
+
+      - name: Build release binaries
+        run: |
+          source /opt/toolchain-v4/activate
+          ./init
+          cd build
+          cmake -DCMAKE_BUILD_TYPE=Release -DMG_EXPERIMENTAL_HIGH_AVAILABILITY=ON ..
+          make -j$THREADS
+      - name: Run unit tests
+        run: |
+          source /opt/toolchain-v4/activate
+          cd build
+          ctest -R memgraph__unit --output-on-failure -j$THREADS
+      - name: Run e2e tests
+        run: |
+          cd tests
+          ./setup.sh /opt/toolchain-v4/activate
+          source ve3/bin/activate_e2e
+          cd e2e
+          ./run.sh "Coordinator"
+          ./run.sh "Client initiated failover"
+          ./run.sh "Uninitialized cluster"
+      - name: Save test data
+        uses: actions/upload-artifact@v3
+        if: always()
+        with:
+          name: "Test data"
+          path: |
+            # multiple paths could be defined
+            build/logs
+
+  experimental_build_mt:
+    name: "MultiTenancy replication build"
+    runs-on: [self-hosted, Linux, X64, Diff]
+    env:
+      THREADS: 24
+      MEMGRAPH_ENTERPRISE_LICENSE: ${{ secrets.MEMGRAPH_ENTERPRISE_LICENSE }}
+      MEMGRAPH_ORGANIZATION_NAME: ${{ secrets.MEMGRAPH_ORGANIZATION_NAME }}
+
+    steps:
+      - name: Set up repository
+        uses: actions/checkout@v3
+        with:
+          # Number of commits to fetch. `0` indicates all history for all
+          # branches and tags. (default: 1)
+          fetch-depth: 0
+
+
+      - name: Build release binaries
+        run: |
+          # Activate toolchain.
+          source /opt/toolchain-v4/activate
+
+          # Initialize dependencies.
+          ./init
+
+          # Build MT replication experimental binaries.
+          cd build
+          cmake -DCMAKE_BUILD_TYPE=Release -D MG_EXPERIMENTAL_REPLICATION_MULTITENANCY=ON ..
+          make -j$THREADS
+
+      - name: Run unit tests
+        run: |
+          # Activate toolchain.
+          source /opt/toolchain-v4/activate
+
+          # Run unit tests.
+          cd build
+          ctest -R memgraph__unit --output-on-failure -j$THREADS
+
+      - name: Run e2e tests
+        run: |
+          cd tests
+          ./setup.sh /opt/toolchain-v4/activate
+          source ve3/bin/activate_e2e
+          cd e2e
+
+          # Just the replication based e2e tests
+          ./run.sh "Replicate multitenancy"
+          ./run.sh "Show"
+          ./run.sh "Show while creating invalid state"
+          ./run.sh "Delete edge replication"
+          ./run.sh "Read-write benchmark"
+          ./run.sh "Index replication"
+          ./run.sh "Constraints"
+
+      - name: Save test data
+        uses: actions/upload-artifact@v3
+        if: always()
+        with:
+          name: "Test data"
+          path: |
+            # multiple paths could be defined
+            build/logs
+
   release_jepsen_test:
     name: "Release Jepsen Test"
     runs-on: [self-hosted, Linux, X64, Debian10, JepsenControl]

.github/workflows/release_debian10.yaml

@@ -281,6 +281,13 @@ jobs:
           cd build
           ctest -R memgraph__unit --output-on-failure
 
+      - name: Ensure Kafka and Pulsar are up
+        run: |
+          cd tests/e2e/streams/kafka
+          docker-compose up -d
+          cd ../pulsar
+          docker-compose up -d
+
       - name: Run e2e tests
         run: |
           cd tests
@@ -289,6 +296,14 @@ jobs:
           cd e2e
           ./run.sh
 
+      - name: Ensure Kafka and Pulsar are down
+        if: always()
+        run: |
+          cd tests/e2e/streams/kafka
+          docker-compose down
+          cd ../pulsar
+          docker-compose down
+
       - name: Run stress test (plain)
         run: |
           cd tests/stress

.github/workflows/release_ubuntu2004.yaml

@@ -281,6 +281,13 @@ jobs:
           cd build
           ctest -R memgraph__unit --output-on-failure
 
+      - name: Ensure Kafka and Pulsar are up
+        run: |
+          cd tests/e2e/streams/kafka
+          docker-compose up -d
+          cd ../pulsar
+          docker-compose up -d
+
       - name: Run e2e tests
         run: |
           cd tests
@@ -289,6 +296,14 @@ jobs:
           cd e2e
           ./run.sh
 
+      - name: Ensure Kafka and Pulsar are down
+        if: always()
+        run: |
+          cd tests/e2e/streams/kafka
+          docker-compose down
+          cd ../pulsar
+          docker-compose down
+
       - name: Run stress test (plain)
         run: |
           cd tests/stress

ADRs/002_nuraft.md

@@ -0,0 +1,34 @@
+# NuRaft ADR
+
+**Author**
+Marko Budiselic (github.com/gitbuda)
+
+**Status**
+PROPOSED
+
+**Date**
+January 10, 2024
+
+**Problem**
+
+In order to enhance Memgraph to have High Availability features as requested by
+customers, we want to have reliable coordinators backed by RAFT consensus algorithm. Implementing
+RAFT to be correct and performant is a very challenging task. Skillful Memgraph
+engineers already tried 3 times and failed to deliver in a reasonable timeframe
+all three times (approximately 4 person-weeks of engineering work each time).
+
+**Criteria**
+
+- easy integration with our C++ codebase
+- heavily tested in production environments
+- implementation of performance optimizations on top of the canonical Raft
+  implementation
+
+**Decision**
+
+There are a few, robust C++ implementations of Raft but as a part of other
+projects or bigger libraries. **We select
+[NuRaft](https://github.com/eBay/NuRaft)** because it focuses on delivering
+Raft without bloatware, and it's used by
+[Clickhouse](https://github.com/ClickHouse/ClickHouse) (an comparable peer to
+Memgraph, a very well-established product).

CMakeLists.txt

@@ -271,6 +271,17 @@ endif()
 set(libs_dir ${CMAKE_SOURCE_DIR}/libs)
 add_subdirectory(libs EXCLUDE_FROM_ALL)
 
+option(MG_EXPERIMENTAL_HIGH_AVAILABILITY "Feature flag for experimental high availability" OFF)
+
+if (NOT MG_ENTERPRISE AND MG_EXPERIMENTAL_HIGH_AVAILABILITY)
+    set(MG_EXPERIMENTAL_HIGH_AVAILABILITY OFF)
+    message(FATAL_ERROR "MG_EXPERIMENTAL_HIGH_AVAILABILITY must be used with enterpise version of the code.")
+endif ()
+
+if (MG_EXPERIMENTAL_HIGH_AVAILABILITY)
+    add_compile_definitions(MG_EXPERIMENTAL_HIGH_AVAILABILITY)
+endif ()
+
 # Optional subproject configuration -------------------------------------------
 option(TEST_COVERAGE "Generate coverage reports from running memgraph" OFF)
 option(TOOLS "Build tools binaries" ON)
@@ -279,6 +290,18 @@ option(ASAN "Build with Address Sanitizer. To get a reasonable performance optio
 option(TSAN "Build with Thread Sanitizer. To get a reasonable performance option should be used only in Release or RelWithDebInfo build " OFF)
 option(UBSAN "Build with Undefined Behaviour Sanitizer" OFF)
 
+# Build feature flags
+option(MG_EXPERIMENTAL_REPLICATION_MULTITENANCY "Feature flag for experimental replicaition of multitenacy" OFF)
+
+if (NOT MG_ENTERPRISE AND MG_EXPERIMENTAL_REPLICATION_MULTITENANCY)
+    set(MG_EXPERIMENTAL_REPLICATION_MULTITENANCY OFF)
+    message(FATAL_ERROR "MG_EXPERIMENTAL_REPLICATION_MULTITENANCY with community edition build isn't possible")
+endif ()
+
+if (MG_EXPERIMENTAL_REPLICATION_MULTITENANCY)
+    add_compile_definitions(MG_EXPERIMENTAL_REPLICATION_MULTITENANCY)
+endif ()
+
 if (TEST_COVERAGE)
   string(TOLOWER ${CMAKE_BUILD_TYPE} lower_build_type)
   if (NOT lower_build_type STREQUAL "debug")

licenses/BSL.txt

@@ -36,7 +36,7 @@ ADDITIONAL USE GRANT:   You may use the Licensed Work in accordance with the
                         3. using the Licensed Work to create a work or solution
                         which competes (or might reasonably be expected to
                         compete) with the Licensed Work.
-CHANGE DATE:            2027-08-12
+CHANGE DATE:            2028-21-01
 CHANGE LICENSE:         Apache License, Version 2.0
 
 For information about alternative licensing arrangements, please visit: https://memgraph.com/legal.

src/CMakeLists.txt

@@ -22,6 +22,8 @@ add_subdirectory(dbms)
 add_subdirectory(flags)
 add_subdirectory(distributed)
 add_subdirectory(replication)
+add_subdirectory(coordination)
+add_subdirectory(replication_coordination_glue)
 
 string(TOLOWER ${CMAKE_BUILD_TYPE} lower_build_type)
 

src/auth/auth.cpp

@@ -255,10 +255,8 @@ void Auth::SaveRole(const Role &role) {
 }
 
 std::optional<Role> Auth::AddRole(const std::string &rolename) {
-  auto existing_role = GetRole(rolename);
-  if (existing_role) return std::nullopt;
-  auto existing_user = GetUser(rolename);
-  if (existing_user) return std::nullopt;
+  if (auto existing_role = GetRole(rolename)) return std::nullopt;
+  if (auto existing_user = GetUser(rolename)) return std::nullopt;
   auto new_role = Role(rolename);
   SaveRole(new_role);
   return new_role;
@@ -285,8 +283,7 @@ std::vector<auth::Role> Auth::AllRoles() const {
   for (auto it = storage_.begin(kRolePrefix); it != storage_.end(kRolePrefix); ++it) {
     auto rolename = it->first.substr(kRolePrefix.size());
     if (rolename != utils::ToLowerCase(rolename)) continue;
-    auto role = GetRole(rolename);
-    if (role) {
+    if (auto role = GetRole(rolename)) {
       ret.push_back(*role);
     } else {
       throw AuthException("Couldn't load role '{}'!", rolename);
@@ -296,15 +293,14 @@ std::vector<auth::Role> Auth::AllRoles() const {
 }
 
 std::vector<auth::User> Auth::AllUsersForRole(const std::string &rolename_orig) const {
-  auto rolename = utils::ToLowerCase(rolename_orig);
+  const auto rolename = utils::ToLowerCase(rolename_orig);
   std::vector<auth::User> ret;
   for (auto it = storage_.begin(kLinkPrefix); it != storage_.end(kLinkPrefix); ++it) {
     auto username = it->first.substr(kLinkPrefix.size());
     if (username != utils::ToLowerCase(username)) continue;
     if (it->second != utils::ToLowerCase(it->second)) continue;
     if (it->second == rolename) {
-      auto user = GetUser(username);
-      if (user) {
+      if (auto user = GetUser(username)) {
         ret.push_back(std::move(*user));
       } else {
         throw AuthException("Couldn't load user '{}'!", username);
@@ -316,8 +312,7 @@ std::vector<auth::User> Auth::AllUsersForRole(const std::string &rolename_orig)
 
 #ifdef MG_ENTERPRISE
 bool Auth::GrantDatabaseToUser(const std::string &db, const std::string &name) {
-  auto user = GetUser(name);
-  if (user) {
+  if (auto user = GetUser(name)) {
     if (db == kAllDatabases) {
       user->db_access().GrantAll();
     } else {
@@ -330,8 +325,7 @@ bool Auth::GrantDatabaseToUser(const std::string &db, const std::string &name) {
 }
 
 bool Auth::RevokeDatabaseFromUser(const std::string &db, const std::string &name) {
-  auto user = GetUser(name);
-  if (user) {
+  if (auto user = GetUser(name)) {
     if (db == kAllDatabases) {
       user->db_access().DenyAll();
     } else {
@@ -346,17 +340,15 @@ bool Auth::RevokeDatabaseFromUser(const std::string &db, const std::string &name
 void Auth::DeleteDatabase(const std::string &db) {
   for (auto it = storage_.begin(kUserPrefix); it != storage_.end(kUserPrefix); ++it) {
     auto username = it->first.substr(kUserPrefix.size());
-    auto user = GetUser(username);
-    if (user) {
+    if (auto user = GetUser(username)) {
       user->db_access().Delete(db);
       SaveUser(*user);
     }
   }
 }
 
-bool Auth::SetMainDatabase(const std::string &db, const std::string &name) {
-  auto user = GetUser(name);
-  if (user) {
+bool Auth::SetMainDatabase(std::string_view db, const std::string &name) {
+  if (auto user = GetUser(name)) {
     if (!user->db_access().SetDefault(db)) {
       throw AuthException("Couldn't set default database '{}' for user '{}'!", db, name);
     }

src/auth/auth.hpp

@@ -195,7 +195,7 @@ class Auth final {
    * @return true on success
    * @throw AuthException if unable to find or update the user
    */
-  bool SetMainDatabase(const std::string &db, const std::string &name);
+  bool SetMainDatabase(std::string_view db, const std::string &name);
 #endif
 
  private:

src/auth/models.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Licensed as a Memgraph Enterprise file under the Memgraph Enterprise
 // License (the "License"); by using this file, you agree to be bound by the terms of the License, and you may not use
@@ -62,7 +62,8 @@ const std::vector<Permission> kPermissionsAll = {Permission::MATCH,
                                                  Permission::TRANSACTION_MANAGEMENT,
                                                  Permission::STORAGE_MODE,
                                                  Permission::MULTI_DATABASE_EDIT,
-                                                 Permission::MULTI_DATABASE_USE};
+                                                 Permission::MULTI_DATABASE_USE,
+                                                 Permission::COORDINATOR};
 
 }  // namespace
 
@@ -118,6 +119,8 @@ std::string PermissionToString(Permission permission) {
       return "MULTI_DATABASE_EDIT";
     case Permission::MULTI_DATABASE_USE:
       return "MULTI_DATABASE_USE";
+    case Permission::COORDINATOR:
+      return "COORDINATOR";
   }
 }
 
@@ -486,13 +489,13 @@ bool operator==(const Role &first, const Role &second) {
 }
 
 #ifdef MG_ENTERPRISE
-void Databases::Add(const std::string &db) {
+void Databases::Add(std::string_view db) {
   if (allow_all_) {
     grants_dbs_.clear();
     allow_all_ = false;
   }
   grants_dbs_.emplace(db);
-  denies_dbs_.erase(db);
+  denies_dbs_.erase(std::string{db});  // TODO: C++23 use transparent key compare
 }
 
 void Databases::Remove(const std::string &db) {
@@ -523,13 +526,13 @@ void Databases::DenyAll() {
   denies_dbs_.clear();
 }
 
-bool Databases::SetDefault(const std::string &db) {
+bool Databases::SetDefault(std::string_view db) {
   if (!Contains(db)) return false;
   default_db_ = db;
   return true;
 }
 
-[[nodiscard]] bool Databases::Contains(const std::string &db) const {
+[[nodiscard]] bool Databases::Contains(std::string_view db) const {
   return !denies_dbs_.contains(db) && (allow_all_ || grants_dbs_.contains(db));
 }
 

src/auth/models.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Licensed as a Memgraph Enterprise file under the Memgraph Enterprise
 // License (the "License"); by using this file, you agree to be bound by the terms of the License, and you may not use
@@ -48,6 +48,7 @@ enum class Permission : uint64_t {
   STORAGE_MODE = 1U << 22U,
   MULTI_DATABASE_EDIT = 1U << 23U,
   MULTI_DATABASE_USE  = 1U << 24U,
+  COORDINATOR  = 1U << 25U,
 };
 // clang-format on
 
@@ -246,7 +247,7 @@ bool operator==(const Role &first, const Role &second);
 #ifdef MG_ENTERPRISE
 class Databases final {
  public:
-  Databases() : grants_dbs_({dbms::kDefaultDB}), allow_all_(false), default_db_(dbms::kDefaultDB) {}
+  Databases() : grants_dbs_{std::string{dbms::kDefaultDB}}, allow_all_(false), default_db_(dbms::kDefaultDB) {}
 
   Databases(const Databases &) = default;
   Databases &operator=(const Databases &) = default;
@@ -259,7 +260,7 @@ class Databases final {
    *
    * @param db name of the database to grant access to
    */
-  void Add(const std::string &db);
+  void Add(std::string_view db);
 
   /**
    * @brief Remove database to the list of granted access.
@@ -291,7 +292,7 @@ class Databases final {
   /**
    * @brief Set the default database.
    */
-  bool SetDefault(const std::string &db);
+  bool SetDefault(std::string_view db);
 
   /**
    * @brief Checks if access is grated to the database.
@@ -299,7 +300,7 @@ class Databases final {
    * @param db name of the database
    * @return true if allow_all and not denied or granted
    */
-  bool Contains(const std::string &db) const;
+  bool Contains(std::string_view db) const;
 
   bool GetAllowAll() const { return allow_all_; }
   const std::set<std::string, std::less<>> &GetGrants() const { return grants_dbs_; }
@@ -312,7 +313,7 @@ class Databases final {
 
  private:
   Databases(bool allow_all, std::set<std::string, std::less<>> grant, std::set<std::string, std::less<>> deny,
-            std::string default_db = dbms::kDefaultDB)
+            std::string default_db = std::string{dbms::kDefaultDB})
       : grants_dbs_(std::move(grant)),
         denies_dbs_(std::move(deny)),
         allow_all_(allow_all),

src/communication/bolt/v1/states/handlers.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -170,6 +170,7 @@ inline State HandleFailure(TSession &session, const std::exception &e) {
     spdlog::trace("Error trace: {}", p->trace());
   }
   session.encoder_buffer_.Clear();
+
   auto code_message = ExceptionToErrorMessage(e);
   bool fail_sent = session.encoder_.MessageFailure({{"code", code_message.first}, {"message", code_message.second}});
   if (!fail_sent) {

src/communication/result_stream_faker.hpp

@@ -44,7 +44,7 @@ class ResultStreamFaker {
     std::vector<memgraph::communication::bolt::Value> bvalues;
     bvalues.reserve(values.size());
     for (const auto &value : values) {
-      auto maybe_value = memgraph::glue::ToBoltValue(value, *store_, memgraph::storage::View::NEW);
+      auto maybe_value = memgraph::glue::ToBoltValue(value, store_, memgraph::storage::View::NEW);
       MG_ASSERT(maybe_value.HasValue());
       bvalues.push_back(std::move(*maybe_value));
     }
@@ -56,7 +56,7 @@ class ResultStreamFaker {
   void Summary(const std::map<std::string, memgraph::query::TypedValue> &summary) {
     std::map<std::string, memgraph::communication::bolt::Value> bsummary;
     for (const auto &item : summary) {
-      auto maybe_value = memgraph::glue::ToBoltValue(item.second, *store_, memgraph::storage::View::NEW);
+      auto maybe_value = memgraph::glue::ToBoltValue(item.second, store_, memgraph::storage::View::NEW);
       MG_ASSERT(maybe_value.HasValue());
       bsummary.insert({item.first, std::move(*maybe_value)});
     }

src/coordination/CMakeLists.txt

@@ -0,0 +1,30 @@
+add_library(mg-coordination STATIC)
+add_library(mg::coordination ALIAS mg-coordination)
+target_sources(mg-coordination
+        PUBLIC
+        include/coordination/coordinator_client.hpp
+        include/coordination/coordinator_state.hpp
+        include/coordination/coordinator_rpc.hpp
+        include/coordination/coordinator_server.hpp
+        include/coordination/coordinator_config.hpp
+        include/coordination/coordinator_exceptions.hpp
+        include/coordination/coordinator_instance.hpp
+        include/coordination/coordinator_slk.hpp
+        include/coordination/coordinator_data.hpp
+        include/coordination/constants.hpp
+        include/coordination/failover_status.hpp
+        include/coordination/coordinator_cluster_config.hpp
+
+        PRIVATE
+        coordinator_client.cpp
+        coordinator_state.cpp
+        coordinator_rpc.cpp
+        coordinator_server.cpp
+        coordinator_data.cpp
+        coordinator_instance.cpp
+)
+target_include_directories(mg-coordination PUBLIC include)
+
+target_link_libraries(mg-coordination
+    PUBLIC mg::utils mg::rpc mg::slk mg::io mg::repl_coord_glue lib::rangev3
+)

src/coordination/coordinator_client.cpp

@@ -0,0 +1,106 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_client.hpp"
+
+#include "coordination/coordinator_config.hpp"
+#include "coordination/coordinator_rpc.hpp"
+#include "replication_coordination_glue/messages.hpp"
+
+namespace memgraph::coordination {
+
+namespace {
+auto CreateClientContext(const memgraph::coordination::CoordinatorClientConfig &config)
+    -> communication::ClientContext {
+  return (config.ssl) ? communication::ClientContext{config.ssl->key_file, config.ssl->cert_file}
+                      : communication::ClientContext{};
+}
+}  // namespace
+
+CoordinatorClient::CoordinatorClient(CoordinatorData *coord_data, CoordinatorClientConfig config,
+                                     HealthCheckCallback succ_cb, HealthCheckCallback fail_cb)
+    : rpc_context_{CreateClientContext(config)},
+      rpc_client_{io::network::Endpoint(io::network::Endpoint::needs_resolving, config.ip_address, config.port),
+                  &rpc_context_},
+      config_{std::move(config)},
+      coord_data_{coord_data},
+      succ_cb_{std::move(succ_cb)},
+      fail_cb_{std::move(fail_cb)} {}
+
+auto CoordinatorClient::InstanceName() const -> std::string { return config_.instance_name; }
+auto CoordinatorClient::SocketAddress() const -> std::string { return rpc_client_.Endpoint().SocketAddress(); }
+
+void CoordinatorClient::StartFrequentCheck() {
+  MG_ASSERT(config_.health_check_frequency_sec > std::chrono::seconds(0),
+            "Health check frequency must be greater than 0");
+
+  instance_checker_.Run(
+      config_.instance_name, config_.health_check_frequency_sec, [this, instance_name = config_.instance_name] {
+        try {
+          spdlog::trace("Sending frequent heartbeat to machine {} on {}", instance_name,
+                        rpc_client_.Endpoint().SocketAddress());
+          auto stream{rpc_client_.Stream<memgraph::replication_coordination_glue::FrequentHeartbeatRpc>()};
+          stream.AwaitResponse();
+          succ_cb_(coord_data_, instance_name);
+        } catch (const rpc::RpcFailedException &) {
+          fail_cb_(coord_data_, instance_name);
+        }
+      });
+}
+
+void CoordinatorClient::StopFrequentCheck() { instance_checker_.Stop(); }
+void CoordinatorClient::PauseFrequentCheck() { instance_checker_.Pause(); }
+void CoordinatorClient::ResumeFrequentCheck() { instance_checker_.Resume(); }
+
+auto CoordinatorClient::SetCallbacks(HealthCheckCallback succ_cb, HealthCheckCallback fail_cb) -> void {
+  succ_cb_ = std::move(succ_cb);
+  fail_cb_ = std::move(fail_cb);
+}
+
+auto CoordinatorClient::ReplicationClientInfo() const -> CoordinatorClientConfig::ReplicationClientInfo {
+  return config_.replication_client_info;
+}
+
+auto CoordinatorClient::SendPromoteReplicaToMainRpc(
+    std::vector<CoordinatorClientConfig::ReplicationClientInfo> replication_clients_info) const -> bool {
+  try {
+    auto stream{rpc_client_.Stream<PromoteReplicaToMainRpc>(std::move(replication_clients_info))};
+    if (!stream.AwaitResponse().success) {
+      spdlog::error("Failed to receive successful RPC failover response!");
+      return false;
+    }
+    return true;
+  } catch (const rpc::RpcFailedException &) {
+    spdlog::error("RPC error occurred while sending failover RPC!");
+  }
+  return false;
+}
+
+auto CoordinatorClient::DemoteToReplica() const -> bool {
+  const auto instance_name = config_.instance_name;
+  try {
+    auto stream{rpc_client_.Stream<SetMainToReplicaRpc>(config_.replication_client_info)};
+    if (!stream.AwaitResponse().success) {
+      spdlog::error("Failed to receive successful RPC response for setting instance {} to replica!", instance_name);
+      return false;
+    }
+    spdlog::info("Sent request RPC from coordinator to instance to set it as replica!");
+    return true;
+  } catch (const rpc::RpcFailedException &) {
+    spdlog::error("Failed to set instance {} to replica!", instance_name);
+  }
+  return false;
+}
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/coordinator_data.cpp

@@ -0,0 +1,224 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#include "coordination/coordinator_instance.hpp"
+#include "coordination/register_main_replica_coordinator_status.hpp"
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_data.hpp"
+
+#include <range/v3/view.hpp>
+#include <shared_mutex>
+
+namespace memgraph::coordination {
+
+CoordinatorData::CoordinatorData() {
+  auto find_instance = [](CoordinatorData *coord_data, std::string_view instance_name) -> CoordinatorInstance & {
+    auto instance = std::ranges::find_if(
+        coord_data->registered_instances_,
+        [instance_name](const CoordinatorInstance &instance) { return instance.InstanceName() == instance_name; });
+
+    MG_ASSERT(instance != coord_data->registered_instances_.end(), "Instance {} not found during callback!",
+              instance_name);
+    return *instance;
+  };
+
+  replica_succ_cb_ = [find_instance](CoordinatorData *coord_data, std::string_view instance_name) -> void {
+    auto lock = std::lock_guard{coord_data->coord_data_lock_};
+    spdlog::trace("Instance {} performing replica successful callback", instance_name);
+    auto &instance = find_instance(coord_data, instance_name);
+    instance.OnSuccessPing();
+  };
+
+  replica_fail_cb_ = [find_instance](CoordinatorData *coord_data, std::string_view instance_name) -> void {
+    auto lock = std::lock_guard{coord_data->coord_data_lock_};
+    spdlog::trace("Instance {} performing replica failure callback", instance_name);
+    auto &instance = find_instance(coord_data, instance_name);
+    instance.OnFailPing();
+  };
+
+  main_succ_cb_ = [this, find_instance](CoordinatorData *coord_data, std::string_view instance_name) -> void {
+    auto lock = std::lock_guard{coord_data->coord_data_lock_};
+    spdlog::trace("Instance {} performing main successful callback", instance_name);
+
+    auto &instance = find_instance(coord_data, instance_name);
+
+    if (instance.IsAlive()) {
+      instance.OnSuccessPing();
+    } else {
+      auto const new_role = coord_data->ClusterHasAliveMain() ? replication_coordination_glue::ReplicationRole::REPLICA
+                                                              : replication_coordination_glue::ReplicationRole::MAIN;
+      if (new_role == replication_coordination_glue::ReplicationRole::REPLICA) {
+        thread_pool_.AddTask([&instance, coord_data, instance_name]() {
+          auto lock = std::lock_guard{coord_data->coord_data_lock_};
+          spdlog::info("Demoting instance {} to replica", instance_name);
+          instance.PauseFrequentCheck();
+          utils::OnScopeExit scope_exit{[&instance] { instance.ResumeFrequentCheck(); }};
+          auto const status = instance.DemoteToReplica(coord_data->replica_succ_cb_, coord_data->replica_fail_cb_);
+          if (!status) {
+            spdlog::error("Instance {} failed to demote to replica", instance_name);
+          } else {
+            spdlog::info("Instance {} demoted to replica", instance_name);
+            instance.OnSuccessPing();
+          }
+        });
+      } else {
+        instance.OnSuccessPing();
+      }
+    }
+  };
+
+  main_fail_cb_ = [this, find_instance](CoordinatorData *coord_data, std::string_view instance_name) -> void {
+    auto lock = std::lock_guard{coord_data->coord_data_lock_};
+    spdlog::trace("Instance {} performing main failure callback", instance_name);
+    auto &instance = find_instance(coord_data, instance_name);
+    instance.OnFailPing();
+
+    if (!ClusterHasAliveMain()) {
+      spdlog::info("Cluster without main instance, starting automatic failover");
+      switch (auto failover_status = DoFailover(); failover_status) {
+        using enum DoFailoverStatus;
+        case ALL_REPLICAS_DOWN:
+          spdlog::warn("Failover aborted since all replicas are down!");
+          break;
+        case MAIN_ALIVE:
+          spdlog::warn("Failover aborted since main is alive!");
+          break;
+        case RPC_FAILED:
+          spdlog::warn("Failover aborted since promoting replica to main failed!");
+          break;
+        case SUCCESS:
+          break;
+      }
+    }
+  };
+}
+
+auto CoordinatorData::ClusterHasAliveMain() const -> bool {
+  auto const alive_main = [](const CoordinatorInstance &instance) { return instance.IsMain() && instance.IsAlive(); };
+  return std::ranges::any_of(registered_instances_, alive_main);
+}
+
+auto CoordinatorData::DoFailover() -> DoFailoverStatus {
+  auto replica_instances = registered_instances_ | ranges::views::filter(&CoordinatorInstance::IsReplica);
+
+  auto chosen_replica_instance = std::ranges::find_if(replica_instances, &CoordinatorInstance::IsAlive);
+  if (chosen_replica_instance == replica_instances.end()) {
+    return DoFailoverStatus::ALL_REPLICAS_DOWN;
+  }
+
+  chosen_replica_instance->PauseFrequentCheck();
+  utils::OnScopeExit scope_exit{[&chosen_replica_instance] { chosen_replica_instance->ResumeFrequentCheck(); }};
+
+  std::vector<ReplClientInfo> repl_clients_info;
+  repl_clients_info.reserve(std::ranges::distance(replica_instances));
+
+  auto const not_chosen_replica_instance = [&chosen_replica_instance](const CoordinatorInstance &instance) {
+    return instance != *chosen_replica_instance;
+  };
+
+  std::ranges::transform(replica_instances | ranges::views::filter(not_chosen_replica_instance),
+                         std::back_inserter(repl_clients_info),
+                         [](const CoordinatorInstance &instance) { return instance.ReplicationClientInfo(); });
+
+  if (!chosen_replica_instance->PromoteToMain(std::move(repl_clients_info), main_succ_cb_, main_fail_cb_)) {
+    return DoFailoverStatus::RPC_FAILED;
+  }
+  return DoFailoverStatus::SUCCESS;
+}
+
+auto CoordinatorData::ShowInstances() const -> std::vector<CoordinatorInstanceStatus> {
+  std::vector<CoordinatorInstanceStatus> instances_status;
+  instances_status.reserve(registered_instances_.size());
+
+  auto const stringify_repl_role = [](const CoordinatorInstance &instance) -> std::string {
+    if (!instance.IsAlive()) return "unknown";
+    if (instance.IsMain()) return "main";
+    return "replica";
+  };
+
+  auto const instance_to_status =
+      [&stringify_repl_role](const CoordinatorInstance &instance) -> CoordinatorInstanceStatus {
+    return {.instance_name = instance.InstanceName(),
+            .socket_address = instance.SocketAddress(),
+            .replication_role = stringify_repl_role(instance),
+            .is_alive = instance.IsAlive()};
+  };
+
+  {
+    auto lock = std::shared_lock{coord_data_lock_};
+    std::ranges::transform(registered_instances_, std::back_inserter(instances_status), instance_to_status);
+  }
+
+  return instances_status;
+}
+
+auto CoordinatorData::SetInstanceToMain(std::string instance_name) -> SetInstanceToMainCoordinatorStatus {
+  auto lock = std::lock_guard{coord_data_lock_};
+
+  auto const is_new_main = [&instance_name](const CoordinatorInstance &instance) {
+    return instance.InstanceName() == instance_name;
+  };
+  auto new_main = std::ranges::find_if(registered_instances_, is_new_main);
+
+  if (new_main == registered_instances_.end()) {
+    spdlog::error("Instance {} not registered. Please register it using REGISTER INSTANCE {}", instance_name,
+                  instance_name);
+    return SetInstanceToMainCoordinatorStatus::NO_INSTANCE_WITH_NAME;
+  }
+
+  new_main->PauseFrequentCheck();
+  utils::OnScopeExit scope_exit{[&new_main] { new_main->ResumeFrequentCheck(); }};
+
+  std::vector<CoordinatorClientConfig::ReplicationClientInfo> repl_clients_info;
+  repl_clients_info.reserve(registered_instances_.size() - 1);
+
+  auto const is_not_new_main = [&instance_name](const CoordinatorInstance &instance) {
+    return instance.InstanceName() != instance_name;
+  };
+  std::ranges::transform(registered_instances_ | ranges::views::filter(is_not_new_main),
+                         std::back_inserter(repl_clients_info),
+                         [](const CoordinatorInstance &instance) { return instance.ReplicationClientInfo(); });
+
+  if (!new_main->PromoteToMain(std::move(repl_clients_info), main_succ_cb_, main_fail_cb_)) {
+    return SetInstanceToMainCoordinatorStatus::COULD_NOT_PROMOTE_TO_MAIN;
+  }
+
+  spdlog::info("Instance {} promoted to main", instance_name);
+  return SetInstanceToMainCoordinatorStatus::SUCCESS;
+}
+
+auto CoordinatorData::RegisterInstance(CoordinatorClientConfig config) -> RegisterInstanceCoordinatorStatus {
+  auto lock = std::lock_guard{coord_data_lock_};
+  if (std::ranges::any_of(registered_instances_, [&config](const CoordinatorInstance &instance) {
+        return instance.InstanceName() == config.instance_name;
+      })) {
+    return RegisterInstanceCoordinatorStatus::NAME_EXISTS;
+  }
+
+  if (std::ranges::any_of(registered_instances_, [&config](const CoordinatorInstance &instance) {
+        return instance.SocketAddress() == config.SocketAddress();
+      })) {
+    return RegisterInstanceCoordinatorStatus::END_POINT_EXISTS;
+  }
+
+  try {
+    registered_instances_.emplace_back(this, std::move(config), replica_succ_cb_, replica_fail_cb_);
+    return RegisterInstanceCoordinatorStatus::SUCCESS;
+
+  } catch (CoordinatorRegisterInstanceException const &) {
+    return RegisterInstanceCoordinatorStatus::RPC_FAILED;
+  }
+}
+
+}  // namespace memgraph::coordination
+
+#endif

src/coordination/coordinator_instance.cpp

@@ -0,0 +1,84 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_instance.hpp"
+
+namespace memgraph::coordination {
+
+CoordinatorInstance::CoordinatorInstance(CoordinatorData *data, CoordinatorClientConfig config,
+                                         HealthCheckCallback succ_cb, HealthCheckCallback fail_cb)
+    : client_(data, std::move(config), std::move(succ_cb), std::move(fail_cb)),
+      replication_role_(replication_coordination_glue::ReplicationRole::REPLICA),
+      is_alive_(true) {
+  if (!client_.DemoteToReplica()) {
+    throw CoordinatorRegisterInstanceException("Failed to demote instance {} to replica", client_.InstanceName());
+  }
+  client_.StartFrequentCheck();
+}
+
+auto CoordinatorInstance::OnSuccessPing() -> void {
+  last_response_time_ = std::chrono::system_clock::now();
+  is_alive_ = true;
+}
+
+auto CoordinatorInstance::OnFailPing() -> bool {
+  is_alive_ =
+      std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now() - last_response_time_).count() <
+      CoordinatorClusterConfig::alive_response_time_difference_sec_;
+  return is_alive_;
+}
+
+auto CoordinatorInstance::InstanceName() const -> std::string { return client_.InstanceName(); }
+auto CoordinatorInstance::SocketAddress() const -> std::string { return client_.SocketAddress(); }
+auto CoordinatorInstance::IsAlive() const -> bool { return is_alive_; }
+
+auto CoordinatorInstance::IsReplica() const -> bool {
+  return replication_role_ == replication_coordination_glue::ReplicationRole::REPLICA;
+}
+auto CoordinatorInstance::IsMain() const -> bool {
+  return replication_role_ == replication_coordination_glue::ReplicationRole::MAIN;
+}
+
+auto CoordinatorInstance::PromoteToMain(ReplicationClientsInfo repl_clients_info, HealthCheckCallback main_succ_cb,
+                                        HealthCheckCallback main_fail_cb) -> bool {
+  if (!client_.SendPromoteReplicaToMainRpc(std::move(repl_clients_info))) {
+    return false;
+  }
+
+  replication_role_ = replication_coordination_glue::ReplicationRole::MAIN;
+  client_.SetCallbacks(std::move(main_succ_cb), std::move(main_fail_cb));
+
+  return true;
+}
+
+auto CoordinatorInstance::DemoteToReplica(HealthCheckCallback replica_succ_cb, HealthCheckCallback replica_fail_cb)
+    -> bool {
+  if (!client_.DemoteToReplica()) {
+    return false;
+  }
+
+  replication_role_ = replication_coordination_glue::ReplicationRole::REPLICA;
+  client_.SetCallbacks(std::move(replica_succ_cb), std::move(replica_fail_cb));
+
+  return true;
+}
+
+auto CoordinatorInstance::PauseFrequentCheck() -> void { client_.PauseFrequentCheck(); }
+auto CoordinatorInstance::ResumeFrequentCheck() -> void { client_.ResumeFrequentCheck(); }
+
+auto CoordinatorInstance::ReplicationClientInfo() const -> CoordinatorClientConfig::ReplicationClientInfo {
+  return client_.ReplicationClientInfo();
+}
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/coordinator_rpc.cpp

@@ -0,0 +1,107 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_rpc.hpp"
+
+#include "coordination/coordinator_slk.hpp"
+#include "slk/serialization.hpp"
+
+namespace memgraph {
+
+namespace coordination {
+
+void PromoteReplicaToMainReq::Save(const PromoteReplicaToMainReq &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self, builder);
+}
+
+void PromoteReplicaToMainReq::Load(PromoteReplicaToMainReq *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(self, reader);
+}
+
+void PromoteReplicaToMainRes::Save(const PromoteReplicaToMainRes &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self, builder);
+}
+
+void PromoteReplicaToMainRes::Load(PromoteReplicaToMainRes *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(self, reader);
+}
+
+void SetMainToReplicaReq::Save(const SetMainToReplicaReq &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self, builder);
+}
+
+void SetMainToReplicaReq::Load(SetMainToReplicaReq *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(self, reader);
+}
+
+void SetMainToReplicaRes::Save(const SetMainToReplicaRes &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self, builder);
+}
+
+void SetMainToReplicaRes::Load(SetMainToReplicaRes *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(self, reader);
+}
+
+}  // namespace coordination
+
+constexpr utils::TypeInfo coordination::PromoteReplicaToMainReq::kType{utils::TypeId::COORD_FAILOVER_REQ,
+                                                                       "CoordPromoteReplicaToMainReq", nullptr};
+
+constexpr utils::TypeInfo coordination::PromoteReplicaToMainRes::kType{utils::TypeId::COORD_FAILOVER_RES,
+                                                                       "CoordPromoteReplicaToMainRes", nullptr};
+
+constexpr utils::TypeInfo coordination::SetMainToReplicaReq::kType{utils::TypeId::COORD_SET_REPL_MAIN_REQ,
+                                                                   "CoordDemoteToReplicaReq", nullptr};
+
+constexpr utils::TypeInfo coordination::SetMainToReplicaRes::kType{utils::TypeId::COORD_SET_REPL_MAIN_RES,
+                                                                   "CoordDemoteToReplicaRes", nullptr};
+
+namespace slk {
+
+void Save(const memgraph::coordination::PromoteReplicaToMainRes &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self.success, builder);
+}
+
+void Load(memgraph::coordination::PromoteReplicaToMainRes *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(&self->success, reader);
+}
+
+void Save(const memgraph::coordination::PromoteReplicaToMainReq &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self.replication_clients_info, builder);
+}
+
+void Load(memgraph::coordination::PromoteReplicaToMainReq *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(&self->replication_clients_info, reader);
+}
+
+void Save(const memgraph::coordination::SetMainToReplicaReq &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self.replication_client_info, builder);
+}
+
+void Load(memgraph::coordination::SetMainToReplicaReq *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(&self->replication_client_info, reader);
+}
+
+void Save(const memgraph::coordination::SetMainToReplicaRes &self, memgraph::slk::Builder *builder) {
+  memgraph::slk::Save(self.success, builder);
+}
+
+void Load(memgraph::coordination::SetMainToReplicaRes *self, memgraph::slk::Reader *reader) {
+  memgraph::slk::Load(&self->success, reader);
+}
+
+}  // namespace slk
+
+}  // namespace memgraph
+
+#endif

src/coordination/coordinator_server.cpp

@@ -0,0 +1,57 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_server.hpp"
+#include "replication_coordination_glue/messages.hpp"
+
+namespace memgraph::coordination {
+
+namespace {
+
+auto CreateServerContext(const memgraph::coordination::CoordinatorServerConfig &config)
+    -> communication::ServerContext {
+  return (config.ssl) ? communication::ServerContext{config.ssl->key_file, config.ssl->cert_file, config.ssl->ca_file,
+                                                     config.ssl->verify_peer}
+                      : communication::ServerContext{};
+}
+
+// NOTE: The coordinator server doesn't more than 1 processing thread - each replica can
+// have only a single coordinator server. Also, the single-threaded guarantee
+// simplifies the rest of the implementation.
+constexpr auto kCoordinatorServerThreads = 1;
+
+}  // namespace
+
+CoordinatorServer::CoordinatorServer(const CoordinatorServerConfig &config)
+    : rpc_server_context_{CreateServerContext(config)},
+      rpc_server_{io::network::Endpoint{config.ip_address, config.port}, &rpc_server_context_,
+                  kCoordinatorServerThreads} {
+  rpc_server_.Register<replication_coordination_glue::FrequentHeartbeatRpc>([](auto *req_reader, auto *res_builder) {
+    spdlog::debug("Received FrequentHeartbeatRpc on coordinator server");
+    replication_coordination_glue::FrequentHeartbeatHandler(req_reader, res_builder);
+  });
+}
+
+CoordinatorServer::~CoordinatorServer() {
+  if (rpc_server_.IsRunning()) {
+    auto const &endpoint = rpc_server_.endpoint();
+    spdlog::trace("Closing coordinator server on {}:{}", endpoint.address, endpoint.port);
+    rpc_server_.Shutdown();
+  }
+  rpc_server_.AwaitShutdown();
+}
+
+bool CoordinatorServer::Start() { return rpc_server_.Start(); }
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/coordinator_state.cpp

@@ -0,0 +1,89 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_state.hpp"
+
+#include "coordination/coordinator_config.hpp"
+#include "coordination/register_main_replica_coordinator_status.hpp"
+#include "flags/replication.hpp"
+#include "spdlog/spdlog.h"
+#include "utils/logging.hpp"
+#include "utils/variant_helpers.hpp"
+
+#include <algorithm>
+
+namespace memgraph::coordination {
+
+CoordinatorState::CoordinatorState() {
+  MG_ASSERT(!(FLAGS_coordinator && FLAGS_coordinator_server_port),
+            "Instance cannot be a coordinator and have registered coordinator server.");
+
+  spdlog::info("Executing coordinator constructor");
+  if (FLAGS_coordinator_server_port) {
+    spdlog::info("Coordinator server port set");
+    auto const config = CoordinatorServerConfig{
+        .ip_address = kDefaultReplicationServerIp,
+        .port = static_cast<uint16_t>(FLAGS_coordinator_server_port),
+    };
+    spdlog::info("Executing coordinator constructor main replica");
+
+    data_ = CoordinatorMainReplicaData{.coordinator_server_ = std::make_unique<CoordinatorServer>(config)};
+  }
+}
+
+auto CoordinatorState::RegisterInstance(CoordinatorClientConfig config) -> RegisterInstanceCoordinatorStatus {
+  MG_ASSERT(std::holds_alternative<CoordinatorData>(data_),
+            "Coordinator cannot register replica since variant holds wrong alternative");
+
+  return std::visit(
+      memgraph::utils::Overloaded{
+          [](const CoordinatorMainReplicaData & /*coordinator_main_replica_data*/) {
+            return RegisterInstanceCoordinatorStatus::NOT_COORDINATOR;
+          },
+          [config](CoordinatorData &coordinator_data) { return coordinator_data.RegisterInstance(config); }},
+      data_);
+}
+
+auto CoordinatorState::SetInstanceToMain(std::string instance_name) -> SetInstanceToMainCoordinatorStatus {
+  MG_ASSERT(std::holds_alternative<CoordinatorData>(data_),
+            "Coordinator cannot register replica since variant holds wrong alternative");
+
+  return std::visit(
+      memgraph::utils::Overloaded{[](const CoordinatorMainReplicaData & /*coordinator_main_replica_data*/) {
+                                    return SetInstanceToMainCoordinatorStatus::NOT_COORDINATOR;
+                                  },
+                                  [&instance_name](CoordinatorData &coordinator_data) {
+                                    return coordinator_data.SetInstanceToMain(instance_name);
+                                  }},
+      data_);
+}
+
+auto CoordinatorState::ShowInstances() const -> std::vector<CoordinatorInstanceStatus> {
+  MG_ASSERT(std::holds_alternative<CoordinatorData>(data_),
+            "Can't call show instances on data_, as variant holds wrong alternative");
+  return std::get<CoordinatorData>(data_).ShowInstances();
+}
+
+[[nodiscard]] auto CoordinatorState::DoFailover() -> DoFailoverStatus {
+  MG_ASSERT(std::holds_alternative<CoordinatorData>(data_), "Cannot do failover since variant holds wrong alternative");
+  auto &coord_state = std::get<CoordinatorData>(data_);
+  return coord_state.DoFailover();
+}
+
+auto CoordinatorState::GetCoordinatorServer() const -> CoordinatorServer & {
+  MG_ASSERT(std::holds_alternative<CoordinatorMainReplicaData>(data_),
+            "Cannot get coordinator server since variant holds wrong alternative");
+  return *std::get<CoordinatorMainReplicaData>(data_).coordinator_server_;
+}
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/constants.hpp

@@ -0,0 +1,22 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+namespace memgraph::coordination {
+
+#ifdef MG_EXPERIMENTAL_HIGH_AVAILABILITY
+constexpr bool allow_ha = true;
+#else
+constexpr bool allow_ha = false;
+#endif
+
+}  // namespace memgraph::coordination

src/coordination/include/coordination/coordinator_client.hpp

@@ -0,0 +1,72 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_config.hpp"
+#include "rpc/client.hpp"
+#include "utils/scheduler.hpp"
+
+namespace memgraph::coordination {
+
+class CoordinatorData;
+using HealthCheckCallback = std::function<void(CoordinatorData *, std::string_view)>;
+using ReplicationClientsInfo = std::vector<ReplClientInfo>;
+
+class CoordinatorClient {
+ public:
+  explicit CoordinatorClient(CoordinatorData *coord_data_, CoordinatorClientConfig config, HealthCheckCallback succ_cb,
+                             HealthCheckCallback fail_cb);
+
+  ~CoordinatorClient() = default;
+
+  CoordinatorClient(CoordinatorClient &) = delete;
+  CoordinatorClient &operator=(CoordinatorClient const &) = delete;
+
+  CoordinatorClient(CoordinatorClient &&) noexcept = delete;
+  CoordinatorClient &operator=(CoordinatorClient &&) noexcept = delete;
+
+  void StartFrequentCheck();
+  void StopFrequentCheck();
+  void PauseFrequentCheck();
+  void ResumeFrequentCheck();
+
+  auto InstanceName() const -> std::string;
+  auto SocketAddress() const -> std::string;
+
+  [[nodiscard]] auto SendPromoteReplicaToMainRpc(ReplicationClientsInfo replication_clients_info) const -> bool;
+  [[nodiscard]] auto DemoteToReplica() const -> bool;
+
+  auto ReplicationClientInfo() const -> ReplClientInfo;
+
+  auto SetCallbacks(HealthCheckCallback succ_cb, HealthCheckCallback fail_cb) -> void;
+
+  friend bool operator==(CoordinatorClient const &first, CoordinatorClient const &second) {
+    return first.config_ == second.config_;
+  }
+
+ private:
+  utils::Scheduler instance_checker_;
+
+  // TODO: (andi) Pimpl?
+  communication::ClientContext rpc_context_;
+  mutable rpc::Client rpc_client_;
+
+  CoordinatorClientConfig config_;
+  CoordinatorData *coord_data_;
+  HealthCheckCallback succ_cb_;
+  HealthCheckCallback fail_cb_;
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/coordinator_cluster_config.hpp

@@ -0,0 +1,22 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+namespace memgraph::coordination {
+
+struct CoordinatorClusterConfig {
+  static constexpr int alive_response_time_difference_sec_{5};
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/coordinator_config.hpp

@@ -0,0 +1,77 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "replication_coordination_glue/mode.hpp"
+
+#include <chrono>
+#include <cstdint>
+#include <optional>
+#include <string>
+
+namespace memgraph::coordination {
+
+inline constexpr auto *kDefaultReplicationServerIp = "0.0.0.0";
+
+struct CoordinatorClientConfig {
+  std::string instance_name;
+  std::string ip_address;
+  uint16_t port{};
+  std::chrono::seconds health_check_frequency_sec{1};
+
+  auto SocketAddress() const -> std::string { return ip_address + ":" + std::to_string(port); }
+
+  struct ReplicationClientInfo {
+    std::string instance_name;
+    replication_coordination_glue::ReplicationMode replication_mode{};
+    std::string replication_ip_address;
+    uint16_t replication_port{};
+
+    friend bool operator==(ReplicationClientInfo const &, ReplicationClientInfo const &) = default;
+  };
+
+  ReplicationClientInfo replication_client_info;
+
+  struct SSL {
+    std::string key_file;
+    std::string cert_file;
+
+    friend bool operator==(const SSL &, const SSL &) = default;
+  };
+
+  std::optional<SSL> ssl;
+
+  friend bool operator==(CoordinatorClientConfig const &, CoordinatorClientConfig const &) = default;
+};
+
+using ReplClientInfo = CoordinatorClientConfig::ReplicationClientInfo;
+
+struct CoordinatorServerConfig {
+  std::string ip_address;
+  uint16_t port{};
+  struct SSL {
+    std::string key_file;
+    std::string cert_file;
+    std::string ca_file;
+    bool verify_peer{};
+    friend bool operator==(SSL const &, SSL const &) = default;
+  };
+
+  std::optional<SSL> ssl;
+
+  friend bool operator==(CoordinatorServerConfig const &, CoordinatorServerConfig const &) = default;
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/coordinator_data.hpp

@@ -0,0 +1,53 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_instance.hpp"
+#include "coordination/coordinator_instance_status.hpp"
+#include "coordination/coordinator_server.hpp"
+#include "coordination/failover_status.hpp"
+#include "coordination/register_main_replica_coordinator_status.hpp"
+#include "utils/rw_lock.hpp"
+#include "utils/thread_pool.hpp"
+
+#include <list>
+
+namespace memgraph::coordination {
+class CoordinatorData {
+ public:
+  CoordinatorData();
+
+  [[nodiscard]] auto DoFailover() -> DoFailoverStatus;
+
+  [[nodiscard]] auto RegisterInstance(CoordinatorClientConfig config) -> RegisterInstanceCoordinatorStatus;
+  [[nodiscard]] auto SetInstanceToMain(std::string instance_name) -> SetInstanceToMainCoordinatorStatus;
+
+  auto ShowInstances() const -> std::vector<CoordinatorInstanceStatus>;
+
+ private:
+  auto ClusterHasAliveMain() const -> bool;
+
+  mutable utils::RWLock coord_data_lock_{utils::RWLock::Priority::READ};
+  HealthCheckCallback main_succ_cb_, main_fail_cb_, replica_succ_cb_, replica_fail_cb_;
+  // Must be std::list because we rely on pointer stability
+  std::list<CoordinatorInstance> registered_instances_;
+  utils::ThreadPool thread_pool_{1};
+};
+
+struct CoordinatorMainReplicaData {
+  std::unique_ptr<CoordinatorServer> coordinator_server_;
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/coordinator_exceptions.hpp

@@ -0,0 +1,32 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "utils/exceptions.hpp"
+
+namespace memgraph::coordination {
+class CoordinatorRegisterInstanceException final : public utils::BasicException {
+ public:
+  explicit CoordinatorRegisterInstanceException(const std::string_view what) noexcept
+      : BasicException("Failed to create instance: " + std::string(what)) {}
+
+  template <class... Args>
+  explicit CoordinatorRegisterInstanceException(fmt::format_string<Args...> fmt, Args &&...args) noexcept
+      : CoordinatorRegisterInstanceException(fmt::format(fmt, std::forward<Args>(args)...)) {}
+
+  SPECIALIZE_GET_EXCEPTION_NAME(CoordinatorRegisterInstanceException)
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/coordinator_instance.hpp

@@ -0,0 +1,68 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_client.hpp"
+#include "coordination/coordinator_cluster_config.hpp"
+#include "coordination/coordinator_exceptions.hpp"
+#include "replication_coordination_glue/role.hpp"
+
+namespace memgraph::coordination {
+
+class CoordinatorData;
+
+class CoordinatorInstance {
+ public:
+  CoordinatorInstance(CoordinatorData *data, CoordinatorClientConfig config, HealthCheckCallback succ_cb,
+                      HealthCheckCallback fail_cb);
+
+  CoordinatorInstance(CoordinatorInstance const &other) = delete;
+  CoordinatorInstance &operator=(CoordinatorInstance const &other) = delete;
+  CoordinatorInstance(CoordinatorInstance &&other) noexcept = delete;
+  CoordinatorInstance &operator=(CoordinatorInstance &&other) noexcept = delete;
+  ~CoordinatorInstance() = default;
+
+  auto OnSuccessPing() -> void;
+  auto OnFailPing() -> bool;
+
+  auto IsAlive() const -> bool;
+
+  auto InstanceName() const -> std::string;
+  auto SocketAddress() const -> std::string;
+
+  auto IsReplica() const -> bool;
+  auto IsMain() const -> bool;
+
+  auto PromoteToMain(ReplicationClientsInfo repl_clients_info, HealthCheckCallback main_succ_cb,
+                     HealthCheckCallback main_fail_cb) -> bool;
+  auto DemoteToReplica(HealthCheckCallback replica_succ_cb, HealthCheckCallback replica_fail_cb) -> bool;
+
+  auto PauseFrequentCheck() -> void;
+  auto ResumeFrequentCheck() -> void;
+
+  auto ReplicationClientInfo() const -> ReplClientInfo;
+
+ private:
+  CoordinatorClient client_;
+  replication_coordination_glue::ReplicationRole replication_role_;
+  std::chrono::system_clock::time_point last_response_time_{};
+  bool is_alive_{false};
+
+  friend bool operator==(CoordinatorInstance const &first, CoordinatorInstance const &second) {
+    return first.client_ == second.client_ && first.replication_role_ == second.replication_role_;
+  }
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/coordinator_instance_status.hpp

@@ -0,0 +1,31 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "io/network/endpoint.hpp"
+
+#include <string_view>
+
+namespace memgraph::coordination {
+
+struct CoordinatorInstanceStatus {
+  std::string instance_name;
+  std::string socket_address;
+  std::string replication_role;
+  bool is_alive;
+};
+
+}  // namespace memgraph::coordination
+
+#endif

src/coordination/include/coordination/coordinator_rpc.hpp

@@ -0,0 +1,104 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_config.hpp"
+#include "rpc/messages.hpp"
+#include "slk/serialization.hpp"
+
+namespace memgraph::coordination {
+
+struct PromoteReplicaToMainReq {
+  static const utils::TypeInfo kType;
+  static const utils::TypeInfo &GetTypeInfo() { return kType; }
+
+  static void Load(PromoteReplicaToMainReq *self, memgraph::slk::Reader *reader);
+  static void Save(const PromoteReplicaToMainReq &self, memgraph::slk::Builder *builder);
+
+  explicit PromoteReplicaToMainReq(std::vector<CoordinatorClientConfig::ReplicationClientInfo> replication_clients_info)
+      : replication_clients_info(std::move(replication_clients_info)) {}
+  PromoteReplicaToMainReq() = default;
+
+  std::vector<CoordinatorClientConfig::ReplicationClientInfo> replication_clients_info;
+};
+
+struct PromoteReplicaToMainRes {
+  static const utils::TypeInfo kType;
+  static const utils::TypeInfo &GetTypeInfo() { return kType; }
+
+  static void Load(PromoteReplicaToMainRes *self, memgraph::slk::Reader *reader);
+  static void Save(const PromoteReplicaToMainRes &self, memgraph::slk::Builder *builder);
+
+  explicit PromoteReplicaToMainRes(bool success) : success(success) {}
+  PromoteReplicaToMainRes() = default;
+
+  bool success;
+};
+
+using PromoteReplicaToMainRpc = rpc::RequestResponse<PromoteReplicaToMainReq, PromoteReplicaToMainRes>;
+
+struct SetMainToReplicaReq {
+  static const utils::TypeInfo kType;
+  static const utils::TypeInfo &GetTypeInfo() { return kType; }
+
+  static void Load(SetMainToReplicaReq *self, memgraph::slk::Reader *reader);
+  static void Save(const SetMainToReplicaReq &self, memgraph::slk::Builder *builder);
+
+  explicit SetMainToReplicaReq(CoordinatorClientConfig::ReplicationClientInfo replication_client_info)
+      : replication_client_info(std::move(replication_client_info)) {}
+
+  SetMainToReplicaReq() = default;
+
+  CoordinatorClientConfig::ReplicationClientInfo replication_client_info;
+};
+
+struct SetMainToReplicaRes {
+  static const utils::TypeInfo kType;
+  static const utils::TypeInfo &GetTypeInfo() { return kType; }
+
+  static void Load(SetMainToReplicaRes *self, memgraph::slk::Reader *reader);
+  static void Save(const SetMainToReplicaRes &self, memgraph::slk::Builder *builder);
+
+  explicit SetMainToReplicaRes(bool success) : success(success) {}
+  SetMainToReplicaRes() = default;
+
+  bool success;
+};
+
+using SetMainToReplicaRpc = rpc::RequestResponse<SetMainToReplicaReq, SetMainToReplicaRes>;
+
+}  // namespace memgraph::coordination
+
+// SLK serialization declarations
+namespace memgraph::slk {
+
+void Save(const memgraph::coordination::PromoteReplicaToMainRes &self, memgraph::slk::Builder *builder);
+
+void Load(memgraph::coordination::PromoteReplicaToMainRes *self, memgraph::slk::Reader *reader);
+
+void Save(const memgraph::coordination::PromoteReplicaToMainReq &self, memgraph::slk::Builder *builder);
+
+void Load(memgraph::coordination::PromoteReplicaToMainReq *self, memgraph::slk::Reader *reader);
+
+void Save(const memgraph::coordination::SetMainToReplicaRes &self, memgraph::slk::Builder *builder);
+
+void Load(memgraph::coordination::SetMainToReplicaRes *self, memgraph::slk::Reader *reader);
+
+void Save(const memgraph::coordination::SetMainToReplicaReq &self, memgraph::slk::Builder *builder);
+
+void Load(memgraph::coordination::SetMainToReplicaReq *self, memgraph::slk::Reader *reader);
+
+}  // namespace memgraph::slk
+
+#endif

src/coordination/include/coordination/coordinator_server.hpp

@@ -0,0 +1,44 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_config.hpp"
+#include "rpc/server.hpp"
+
+namespace memgraph::coordination {
+
+class CoordinatorServer {
+ public:
+  explicit CoordinatorServer(const CoordinatorServerConfig &config);
+  CoordinatorServer(const CoordinatorServer &) = delete;
+  CoordinatorServer(CoordinatorServer &&) = delete;
+  CoordinatorServer &operator=(const CoordinatorServer &) = delete;
+  CoordinatorServer &operator=(CoordinatorServer &&) = delete;
+
+  virtual ~CoordinatorServer();
+
+  bool Start();
+
+  template <typename TRequestResponse, typename F>
+  void Register(F &&callback) {
+    rpc_server_.Register<TRequestResponse>(std::forward<F>(callback));
+  }
+
+ private:
+  communication::ServerContext rpc_server_context_;
+  rpc::Server rpc_server_;
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/coordinator_slk.hpp

@@ -0,0 +1,38 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_config.hpp"
+#include "slk/serialization.hpp"
+#include "slk/streams.hpp"
+
+namespace memgraph::slk {
+
+using ReplicationClientInfo = coordination::CoordinatorClientConfig::ReplicationClientInfo;
+
+inline void Save(const ReplicationClientInfo &obj, Builder *builder) {
+  Save(obj.instance_name, builder);
+  Save(obj.replication_mode, builder);
+  Save(obj.replication_ip_address, builder);
+  Save(obj.replication_port, builder);
+}
+
+inline void Load(ReplicationClientInfo *obj, Reader *reader) {
+  Load(&obj->instance_name, reader);
+  Load(&obj->replication_mode, reader);
+  Load(&obj->replication_ip_address, reader);
+  Load(&obj->replication_port, reader);
+}
+}  // namespace memgraph::slk
+#endif

src/coordination/include/coordination/coordinator_state.hpp

@@ -0,0 +1,53 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "coordination/coordinator_data.hpp"
+#include "coordination/coordinator_instance_status.hpp"
+#include "coordination/coordinator_server.hpp"
+#include "coordination/failover_status.hpp"
+#include "coordination/register_main_replica_coordinator_status.hpp"
+
+#include <variant>
+
+namespace memgraph::coordination {
+
+class CoordinatorState {
+ public:
+  CoordinatorState();
+  ~CoordinatorState() = default;
+
+  CoordinatorState(const CoordinatorState &) = delete;
+  CoordinatorState &operator=(const CoordinatorState &) = delete;
+
+  CoordinatorState(CoordinatorState &&) noexcept = delete;
+  CoordinatorState &operator=(CoordinatorState &&) noexcept = delete;
+
+  [[nodiscard]] auto RegisterInstance(CoordinatorClientConfig config) -> RegisterInstanceCoordinatorStatus;
+
+  [[nodiscard]] auto SetInstanceToMain(std::string instance_name) -> SetInstanceToMainCoordinatorStatus;
+
+  auto ShowInstances() const -> std::vector<CoordinatorInstanceStatus>;
+
+  // The client code must check that the server exists before calling this method.
+  auto GetCoordinatorServer() const -> CoordinatorServer &;
+
+  [[nodiscard]] auto DoFailover() -> DoFailoverStatus;
+
+ private:
+  std::variant<CoordinatorData, CoordinatorMainReplicaData> data_;
+};
+
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/failover_status.hpp

@@ -0,0 +1,21 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include <cstdint>
+
+namespace memgraph::coordination {
+enum class DoFailoverStatus : uint8_t { SUCCESS, ALL_REPLICAS_DOWN, MAIN_ALIVE, RPC_FAILED };
+}  // namespace memgraph::coordination
+#endif

src/coordination/include/coordination/register_main_replica_coordinator_status.hpp

@@ -0,0 +1,36 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include <cstdint>
+
+namespace memgraph::coordination {
+
+enum class RegisterInstanceCoordinatorStatus : uint8_t {
+  NAME_EXISTS,
+  END_POINT_EXISTS,
+  NOT_COORDINATOR,
+  RPC_FAILED,
+  SUCCESS
+};
+
+enum class SetInstanceToMainCoordinatorStatus : uint8_t {
+  NO_INSTANCE_WITH_NAME,
+  NOT_COORDINATOR,
+  SUCCESS,
+  COULD_NOT_PROMOTE_TO_MAIN,
+};
+
+}  // namespace memgraph::coordination
+#endif

src/dbms/CMakeLists.txt

@@ -1,3 +1,2 @@
-
-add_library(mg-dbms STATIC dbms_handler.cpp database.cpp replication_handler.cpp replication_client.cpp inmemory/replication_handlers.cpp)
-target_link_libraries(mg-dbms mg-utils mg-storage-v2 mg-query)
+add_library(mg-dbms STATIC dbms_handler.cpp database.cpp replication_handler.cpp coordinator_handler.cpp replication_client.cpp inmemory/replication_handlers.cpp coordinator_handlers.cpp)
+target_link_libraries(mg-dbms mg-utils mg-storage-v2 mg-query mg-replication mg-coordination)

src/dbms/constants.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -13,7 +13,8 @@
 
 namespace memgraph::dbms {
 
-constexpr static const char *kDefaultDB = "memgraph";  //!< Name of the default database
+constexpr std::string_view kDefaultDB = "memgraph";        //!< Name of the default database
+constexpr std::string_view kMultiTenantDir = "databases";  //!< Name of the multi-tenant directory
 
 #ifdef MG_EXPERIMENTAL_REPLICATION_MULTITENANCY
 constexpr bool allow_mt_repl = true;

src/dbms/coordinator_handler.cpp

@@ -0,0 +1,38 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#include "coordination/register_main_replica_coordinator_status.hpp"
+#ifdef MG_ENTERPRISE
+
+#include "dbms/coordinator_handler.hpp"
+
+#include "dbms/dbms_handler.hpp"
+
+namespace memgraph::dbms {
+
+CoordinatorHandler::CoordinatorHandler(DbmsHandler &dbms_handler) : dbms_handler_(dbms_handler) {}
+
+auto CoordinatorHandler::RegisterInstance(memgraph::coordination::CoordinatorClientConfig config)
+    -> coordination::RegisterInstanceCoordinatorStatus {
+  return dbms_handler_.CoordinatorState().RegisterInstance(config);
+}
+
+auto CoordinatorHandler::SetInstanceToMain(std::string instance_name)
+    -> coordination::SetInstanceToMainCoordinatorStatus {
+  return dbms_handler_.CoordinatorState().SetInstanceToMain(std::move(instance_name));
+}
+
+auto CoordinatorHandler::ShowInstances() const -> std::vector<coordination::CoordinatorInstanceStatus> {
+  return dbms_handler_.CoordinatorState().ShowInstances();
+}
+}  // namespace memgraph::dbms
+
+#endif

src/dbms/coordinator_handler.hpp

@@ -0,0 +1,47 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "utils/result.hpp"
+
+#include "coordination/coordinator_config.hpp"
+#include "coordination/coordinator_instance_status.hpp"
+#include "coordination/failover_status.hpp"
+#include "coordination/register_main_replica_coordinator_status.hpp"
+
+#include <cstdint>
+#include <optional>
+#include <vector>
+
+namespace memgraph::dbms {
+
+class DbmsHandler;
+
+class CoordinatorHandler {
+ public:
+  explicit CoordinatorHandler(DbmsHandler &dbms_handler);
+
+  auto RegisterInstance(coordination::CoordinatorClientConfig config)
+      -> coordination::RegisterInstanceCoordinatorStatus;
+
+  auto SetInstanceToMain(std::string instance_name) -> coordination::SetInstanceToMainCoordinatorStatus;
+
+  auto ShowInstances() const -> std::vector<coordination::CoordinatorInstanceStatus>;
+
+ private:
+  DbmsHandler &dbms_handler_;
+};
+
+}  // namespace memgraph::dbms
+#endif

src/dbms/coordinator_handlers.cpp

@@ -0,0 +1,155 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#ifdef MG_ENTERPRISE
+
+#include "dbms/coordinator_handlers.hpp"
+#include "dbms/utils.hpp"
+
+#include "coordination/coordinator_exceptions.hpp"
+#include "coordination/coordinator_rpc.hpp"
+#include "dbms/dbms_handler.hpp"
+#include "dbms/replication_client.hpp"
+
+#include "range/v3/view.hpp"
+
+namespace memgraph::dbms {
+
+void CoordinatorHandlers::Register(DbmsHandler &dbms_handler) {
+  auto &server = dbms_handler.CoordinatorState().GetCoordinatorServer();
+
+  server.Register<coordination::PromoteReplicaToMainRpc>(
+      [&dbms_handler](slk::Reader *req_reader, slk::Builder *res_builder) -> void {
+        spdlog::info("Received PromoteReplicaToMainRpc");
+        CoordinatorHandlers::PromoteReplicaToMainHandler(dbms_handler, req_reader, res_builder);
+      });
+
+  server.Register<coordination::SetMainToReplicaRpc>(
+      [&dbms_handler](slk::Reader *req_reader, slk::Builder *res_builder) -> void {
+        spdlog::info("Received SetMainToReplicaRpc from coordinator server");
+        CoordinatorHandlers::SetMainToReplicaHandler(dbms_handler, req_reader, res_builder);
+      });
+}
+
+void CoordinatorHandlers::SetMainToReplicaHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader,
+                                                  slk::Builder *res_builder) {
+  auto &repl_state = dbms_handler.ReplicationState();
+  spdlog::info("Executing SetMainToReplicaHandler");
+
+  if (repl_state.IsReplica()) {
+    spdlog::error("Setting to replica must be performed on main.");
+    slk::Save(coordination::SetMainToReplicaRes{false}, res_builder);
+    return;
+  }
+
+  coordination::SetMainToReplicaReq req;
+  slk::Load(&req, req_reader);
+
+  const replication::ReplicationServerConfig clients_config{
+      .ip_address = req.replication_client_info.replication_ip_address,
+      .port = req.replication_client_info.replication_port};
+
+  if (bool success = memgraph::dbms::SetReplicationRoleReplica(dbms_handler, clients_config); !success) {
+    spdlog::error("Setting main to replica failed!");
+    slk::Save(coordination::PromoteReplicaToMainRes{false}, res_builder);
+    return;
+  }
+
+  slk::Save(coordination::PromoteReplicaToMainRes{true}, res_builder);
+}
+
+void CoordinatorHandlers::PromoteReplicaToMainHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader,
+                                                      slk::Builder *res_builder) {
+  auto &repl_state = dbms_handler.ReplicationState();
+
+  if (!repl_state.IsReplica()) {
+    spdlog::error("Only replica can be promoted to main!");
+    slk::Save(coordination::PromoteReplicaToMainRes{false}, res_builder);
+    return;
+  }
+
+  auto repl_server_config = std::get<replication::RoleReplicaData>(repl_state.ReplicationData()).config;
+
+  // This can fail because of disk. If it does, the cluster state could get inconsistent.
+  // We don't handle disk issues.
+  if (bool success = memgraph::dbms::DoReplicaToMainPromotion(dbms_handler); !success) {
+    spdlog::error("Promoting replica to main failed!");
+    slk::Save(coordination::PromoteReplicaToMainRes{false}, res_builder);
+    return;
+  }
+
+  coordination::PromoteReplicaToMainReq req;
+  slk::Load(&req, req_reader);
+
+  auto const converter = [](const auto &repl_info_config) {
+    return replication::ReplicationClientConfig{
+        .name = repl_info_config.instance_name,
+        .mode = repl_info_config.replication_mode,
+        .ip_address = repl_info_config.replication_ip_address,
+        .port = repl_info_config.replication_port,
+    };
+  };
+
+  MG_ASSERT(
+      std::get<replication::RoleMainData>(repl_state.ReplicationData()).registered_replicas_.empty(),
+      "No replicas should be registered after promoting replica to main and before registering replication clients!");
+
+  // registering replicas
+  for (auto const &config : req.replication_clients_info | ranges::views::transform(converter)) {
+    auto instance_client = repl_state.RegisterReplica(config);
+    if (instance_client.HasError()) {
+      switch (instance_client.GetError()) {
+        // Can't happen, we are already replica
+        case memgraph::replication::RegisterReplicaError::NOT_MAIN:
+          spdlog::error("Failover must be performed to main!");
+          slk::Save(coordination::PromoteReplicaToMainRes{false}, res_builder);
+          return;
+        // Can't happen, checked on the coordinator side
+        case memgraph::replication::RegisterReplicaError::NAME_EXISTS:
+          spdlog::error("Replica with the same name already exists!");
+          slk::Save(coordination::PromoteReplicaToMainRes{false}, res_builder);
+          return;
+        // Can't happen, checked on the coordinator side
+        case memgraph::replication::RegisterReplicaError::ENDPOINT_EXISTS:
+          spdlog::error("Replica with the same endpoint already exists!");
+          slk::Save(coordination::PromoteReplicaToMainRes{false}, res_builder);
+          return;
+        // We don't handle disk issues
+        case memgraph::replication::RegisterReplicaError::COULD_NOT_BE_PERSISTED:
+          spdlog::error("Registered replica could not be persisted!");
+          slk::Save(coordination::PromoteReplicaToMainRes{false}, res_builder);
+          return;
+        case memgraph::replication::RegisterReplicaError::SUCCESS:
+          break;
+      }
+    }
+    if (!allow_mt_repl && dbms_handler.All().size() > 1) {
+      spdlog::warn("Multi-tenant replication is currently not supported!");
+    }
+
+    auto &instance_client_ref = *instance_client.GetValue();
+
+    // Update system before enabling individual storage <-> replica clients
+    dbms_handler.SystemRestore(instance_client_ref);
+
+    // TODO: (andi) Policy for register all databases
+    // Will be resolved after deciding about choosing new replica
+    const bool all_clients_good = memgraph::dbms::RegisterAllDatabasesClients(dbms_handler, instance_client_ref);
+    MG_ASSERT(all_clients_good, "Failed to register one or more databases to the REPLICA \"{}\".", config.name);
+
+    StartReplicaClient(dbms_handler, instance_client_ref);
+  }
+
+  slk::Save(coordination::PromoteReplicaToMainRes{true}, res_builder);
+}
+
+}  // namespace memgraph::dbms
+#endif

src/dbms/coordinator_handlers.hpp

@@ -0,0 +1,34 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#ifdef MG_ENTERPRISE
+
+#include "slk/serialization.hpp"
+
+namespace memgraph::dbms {
+
+class DbmsHandler;
+
+class CoordinatorHandlers {
+ public:
+  static void Register(DbmsHandler &dbms_handler);
+
+ private:
+  static void PromoteReplicaToMainHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader,
+                                          slk::Builder *res_builder);
+  static void SetMainToReplicaHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader, slk::Builder *res_builder);
+};
+
+}  // namespace memgraph::dbms
+
+#endif

src/dbms/database.cpp

@@ -26,7 +26,7 @@ Database::Database(storage::Config config, replication::ReplicationState &repl_s
       streams_{config.durability.storage_directory / "streams"},
       plan_cache_{FLAGS_query_plan_cache_max_size},
       repl_state_(&repl_state) {
-  if (config.storage_mode == memgraph::storage::StorageMode::ON_DISK_TRANSACTIONAL || config.force_on_disk ||
+  if (config.salient.storage_mode == memgraph::storage::StorageMode::ON_DISK_TRANSACTIONAL || config.force_on_disk ||
       utils::DirExists(config.disk.main_storage_directory)) {
     storage_ = std::make_unique<storage::DiskStorage>(std::move(config));
   } else {

src/dbms/database.hpp

@@ -81,7 +81,14 @@ class Database {
    *
    * @return const std::string&
    */
-  const std::string &id() const { return storage_->id(); }
+  const std::string &name() const { return storage_->name(); }
+
+  /**
+   * @brief Unique storage identified (uuid)
+   *
+   * @return const utils::UUID&
+   */
+  const utils::UUID &uuid() const { return storage_->uuid(); }
 
   /**
    * @brief Returns the storage configuration
@@ -103,7 +110,7 @@ class Database {
    * @param force_directory Use the configured directory, do not try to decipher the multi-db version
    * @return DatabaseInfo
    */
-  DatabaseInfo GetInfo(bool force_directory, replication::ReplicationRole replication_role) const {
+  DatabaseInfo GetInfo(bool force_directory, replication_coordination_glue::ReplicationRole replication_role) const {
     DatabaseInfo info;
     info.storage_info = storage_->GetInfo(force_directory, replication_role);
     info.triggers = trigger_store_.GetTriggerInfo().size();

src/dbms/database_handler.hpp

@@ -51,7 +51,7 @@ class DatabaseHandler : public Handler<Database> {
    * @param config Storage configuration
    * @return HandlerT::NewResult
    */
-  HandlerT::NewResult New(std::string_view name, storage::Config config, replication::ReplicationState &repl_state) {
+  HandlerT::NewResult New(storage::Config config, replication::ReplicationState &repl_state) {
     // Control that no one is using the same data directory
     if (std::any_of(begin(), end(), [&](auto &elem) {
           auto db_acc = elem.second.access();
@@ -61,8 +61,7 @@ class DatabaseHandler : public Handler<Database> {
       spdlog::info("Tried to generate new storage using a claimed directory.");
       return NewError::EXISTS;
     }
-    config.name = name;  // Set storage id via config
-    return HandlerT::New(std::piecewise_construct, name, config, repl_state);
+    return HandlerT::New(std::piecewise_construct, config.salient.name, config, repl_state);
   }
 
   /**

src/dbms/dbms_handler.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -11,56 +11,205 @@
 
 #include "dbms/dbms_handler.hpp"
 
+#include "dbms/coordinator_handlers.hpp"
+#include "flags/replication.hpp"
+
+#include <cstdint>
+#include <filesystem>
+
+#include "dbms/constants.hpp"
+#include "dbms/global.hpp"
+#include "dbms/replication_client.hpp"
+#include "spdlog/spdlog.h"
+#include "utils/exceptions.hpp"
+#include "utils/logging.hpp"
+#include "utils/uuid.hpp"
+
 namespace memgraph::dbms {
+
 #ifdef MG_ENTERPRISE
+
+namespace {
+constexpr std::string_view kDBPrefix = "database:";                               // Key prefix for database durability
+constexpr std::string_view kLastCommitedSystemTsKey = "last_commited_system_ts";  // Key for timestamp durability
+}  // namespace
+
+struct Durability {
+  enum class DurabilityVersion : uint8_t {
+    V0 = 0,
+    V1,
+  };
+
+  struct VersionException : public utils::BasicException {
+    VersionException() : utils::BasicException("Unsupported durability version!") {}
+  };
+
+  struct UnknownVersionException : public utils::BasicException {
+    UnknownVersionException() : utils::BasicException("Unable to parse the durability version!") {}
+  };
+
+  struct MigrationException : public utils::BasicException {
+    MigrationException() : utils::BasicException("Failed to migrate to the current durability version!") {}
+  };
+
+  static DurabilityVersion VersionCheck(std::optional<std::string_view> val) {
+    if (!val) {
+      return DurabilityVersion::V0;
+    }
+    if (val == "V1") {
+      return DurabilityVersion::V1;
+    }
+    throw UnknownVersionException();
+  };
+
+  static auto GenKey(std::string_view name) -> std::string { return fmt::format("{}{}", kDBPrefix, name); }
+
+  static auto GenVal(utils::UUID uuid, std::filesystem::path rel_dir) {
+    nlohmann::json json;
+    json["uuid"] = uuid;
+    json["rel_dir"] = rel_dir;
+    // TODO: Serialize the configuration
+    return json.dump();
+  }
+
+  static void Migrate(kvstore::KVStore *durability, const std::filesystem::path &root) {
+    const auto ver_val = durability->Get("version");
+    const auto ver = VersionCheck(ver_val);
+
+    std::map<std::string, std::string> to_put;
+    std::vector<std::string> to_delete;
+
+    // Update from V0 to V1
+    if (ver == DurabilityVersion::V0) {
+      for (const auto &[key, val] : *durability) {
+        if (key == "version") continue;  // Reserved key
+        // Generate a UUID
+        auto const uuid = utils::UUID();
+        // New json values
+        auto new_key = GenKey(key);
+        auto path = root;
+        if (key != kDefaultDB) {  // Special case for non-default DBs
+          // Move directory to new UUID dir
+          path = root / kMultiTenantDir / std::string{uuid};
+          std::filesystem::path old_dir(root / kMultiTenantDir / key);
+          std::error_code ec;
+          std::filesystem::rename(old_dir, path, ec);
+          MG_ASSERT(!ec, "Failed to upgrade durability: cannot move default directory.");
+        }
+        // Generate json and update value
+        auto new_data = GenVal(uuid, std::filesystem::relative(path, root));
+        to_put.emplace(std::move(new_key), std::move(new_data));
+        to_delete.emplace_back(key);
+      }
+    }
+
+    // Set version
+    durability->Put("version", "V1");
+    // Update to the new key-value pairs
+    if (!durability->PutAndDeleteMultiple(to_put, to_delete)) {
+      throw MigrationException();
+    }
+  }
+};
+
 DbmsHandler::DbmsHandler(
     storage::Config config,
     memgraph::utils::Synchronized<memgraph::auth::Auth, memgraph::utils::WritePrioritizedRWLock> *auth,
-    bool recovery_on_startup, bool delete_on_drop)
-    : default_config_{std::move(config)},
-      delete_on_drop_(delete_on_drop),
-      repl_state_{ReplicationStateRootPath(default_config_)} {
+    bool recovery_on_startup)
+    : default_config_{std::move(config)}, repl_state_{ReplicationStateRootPath(default_config_)} {
   // TODO: Decouple storage config from dbms config
   // TODO: Save individual db configs inside the kvstore and restore from there
-  storage::UpdatePaths(default_config_, default_config_.durability.storage_directory / "databases");
-  const auto &db_dir = default_config_.durability.storage_directory;
+
+  /*
+   * FILESYSTEM MANIPULATION
+   */
+  const auto &root = default_config_.durability.storage_directory;
+  storage::UpdatePaths(default_config_, root);
+  const auto &db_dir = default_config_.durability.storage_directory / kMultiTenantDir;
+  // TODO: Unify durability and wal
   const auto durability_dir = db_dir / ".durability";
   utils::EnsureDirOrDie(db_dir);
   utils::EnsureDirOrDie(durability_dir);
   durability_ = std::make_unique<kvstore::KVStore>(durability_dir);
 
-  // Generate the default database
-  MG_ASSERT(!NewDefault_().HasError(), "Failed while creating the default DB.");
+  /*
+   * DURABILITY
+   */
+  // Migrate durability
+  Durability::Migrate(durability_.get(), root);
+  auto directories = std::set{std::string{kDefaultDB}};
 
   // Recover previous databases
   if (recovery_on_startup) {
-    for (const auto &[name, _] : *durability_) {
-      if (name == kDefaultDB) continue;  // Already set
-      spdlog::info("Restoring database {}.", name);
-      MG_ASSERT(!New_(name).HasError(), "Failed while creating database {}.", name);
+    auto it = durability_->begin(std::string(kDBPrefix));
+    auto end = durability_->end(std::string(kDBPrefix));
+    for (; it != end; ++it) {
+      const auto &[key, config_json] = *it;
+      const auto name = key.substr(kDBPrefix.size());
+      auto json = nlohmann::json::parse(config_json);
+      const auto uuid = json.at("uuid").get<utils::UUID>();
+      const auto rel_dir = json.at("rel_dir").get<std::filesystem::path>();
+      spdlog::info("Restoring database {} at {}.", name, rel_dir);
+      auto new_db = New_(name, uuid, rel_dir);
+      MG_ASSERT(!new_db.HasError(), "Failed while creating database {}.", name);
+      directories.emplace(rel_dir.filename());
       spdlog::info("Database {} restored.", name);
     }
+    // Read the last timestamp
+    auto lcst = durability_->Get(kLastCommitedSystemTsKey);
+    if (lcst) {
+      last_commited_system_timestamp_ = std::stoul(*lcst);
+      system_timestamp_ = last_commited_system_timestamp_;
+    }
   } else {  // Clear databases from the durability list and auth
     auto locked_auth = auth->Lock();
-    for (const auto &[name, _] : *durability_) {
+    auto it = durability_->begin(std::string{kDBPrefix});
+    auto end = durability_->end(std::string{kDBPrefix});
+    for (; it != end; ++it) {
+      const auto &[key, _] = *it;
+      const auto name = key.substr(kDBPrefix.size());
       if (name == kDefaultDB) continue;
       locked_auth->DeleteDatabase(name);
-      durability_->Delete(name);
+      durability_->Delete(key);
+    }
+    // Delete the last timestamp
+    durability_->Delete(kLastCommitedSystemTsKey);
+  }
+
+  /*
+   * DATABASES CLEAN UP
+   */
+  // Clean the unused directories
+  for (const auto &entry : std::filesystem::directory_iterator(db_dir)) {
+    const auto &name = entry.path().filename().string();
+    if (entry.is_directory() && !name.empty() && name.front() != '.') {
+      auto itr = directories.find(name);
+      if (itr == directories.end()) {
+        std::error_code dummy;
+        std::filesystem::remove_all(entry, dummy);
+      } else {
+        directories.erase(itr);
+      }
     }
   }
 
+  /*
+   * DEFAULT DB SETUP
+   */
+  // Setup the default DB
+  SetupDefault_();
+
+  /*
+   * REPLICATION RECOVERY AND STARTUP
+   */
   // Startup replication state (if recovered at startup)
-  auto replica = [this](replication::RoleReplicaData const &data) {
-    // Register handlers
-    InMemoryReplicationHandlers::Register(this, *data.server);
-    if (!data.server->Start()) {
-      spdlog::error("Unable to start the replication server.");
-      return false;
-    }
-    return true;
-  };
-  // Replication frequent check start
+  auto replica = [this](replication::RoleReplicaData const &data) { return StartRpcServer(*this, data); };
+  // Replication recovery and frequent check start
   auto main = [this](replication::RoleMainData &data) {
+    for (auto &client : data.registered_replicas_) {
+      SystemRestore(client);
+    }
+    ForEach([this](DatabaseAccess db) { RecoverReplication(db); });
     for (auto &client : data.registered_replicas_) {
       StartReplicaClient(*this, client);
     }
@@ -69,7 +218,232 @@ DbmsHandler::DbmsHandler(
   // Startup proccess for main/replica
   MG_ASSERT(std::visit(memgraph::utils::Overloaded{replica, main}, repl_state_.ReplicationData()),
             "Replica recovery failure!");
-}
-#endif
 
+  // Warning
+  if (default_config_.durability.snapshot_wal_mode == storage::Config::Durability::SnapshotWalMode::DISABLED &&
+      repl_state_.IsMain()) {
+    spdlog::warn(
+        "The instance has the MAIN replication role, but durability logs and snapshots are disabled. Please "
+        "consider "
+        "enabling durability by using --storage-snapshot-interval-sec and --storage-wal-enabled flags because "
+        "without write-ahead logs this instance is not replicating any data.");
+  }
+
+  // MAIN or REPLICA instance
+  if (FLAGS_coordinator_server_port) {
+    CoordinatorHandlers::Register(*this);
+    MG_ASSERT(coordinator_state_.GetCoordinatorServer().Start(), "Failed to start coordinator server!");
+  }
+}
+
+DbmsHandler::DeleteResult DbmsHandler::TryDelete(std::string_view db_name) {
+  std::lock_guard<LockT> wr(lock_);
+  if (db_name == kDefaultDB) {
+    // MSG cannot delete the default db
+    return DeleteError::DEFAULT_DB;
+  }
+
+  // Get DB config for the UUID and disk clean up
+  const auto conf = db_handler_.GetConfig(db_name);
+  if (!conf) {
+    return DeleteError::NON_EXISTENT;
+  }
+  const auto &storage_path = conf->durability.storage_directory;
+  const auto &uuid = conf->salient.uuid;
+
+  // Check if db exists
+  try {
+    // Low level handlers
+    if (!db_handler_.TryDelete(db_name)) {
+      return DeleteError::USING;
+    }
+  } catch (utils::BasicException &) {
+    return DeleteError::NON_EXISTENT;
+  }
+
+  // Remove from durability list
+  if (durability_) durability_->Delete(Durability::GenKey(db_name));
+
+  // Delete disk storage
+  std::error_code ec;
+  (void)std::filesystem::remove_all(storage_path, ec);
+  if (ec) {
+    spdlog::error(R"(Failed to clean disk while deleting database "{}" stored in {})", db_name, storage_path);
+  }
+
+  // Success
+  // Save delta
+  if (system_transaction_) {
+    system_transaction_->delta.emplace(SystemTransaction::Delta::drop_database, uuid);
+  }
+  return {};
+}
+
+DbmsHandler::DeleteResult DbmsHandler::Delete(std::string_view db_name) {
+  auto wr = std::lock_guard(lock_);
+  return Delete_(db_name);
+}
+
+DbmsHandler::DeleteResult DbmsHandler::Delete(utils::UUID uuid) {
+  auto wr = std::lock_guard(lock_);
+  std::string db_name;
+  try {
+    const auto db = Get_(uuid);
+    db_name = db->name();
+  } catch (const UnknownDatabaseException &) {
+    return DeleteError::NON_EXISTENT;
+  }
+  return Delete_(db_name);
+}
+
+DbmsHandler::NewResultT DbmsHandler::New_(storage::Config storage_config) {
+  auto new_db = db_handler_.New(storage_config, repl_state_);
+
+  if (new_db.HasValue()) {  // Success
+                            // Save delta
+    if (system_transaction_) {
+      system_transaction_->delta.emplace(SystemTransaction::Delta::create_database, storage_config.salient);
+    }
+    UpdateDurability(storage_config);
+    return new_db.GetValue();
+  }
+  return new_db.GetError();
+}
+
+DbmsHandler::DeleteResult DbmsHandler::Delete_(std::string_view db_name) {
+  if (db_name == kDefaultDB) {
+    // MSG cannot delete the default db
+    return DeleteError::DEFAULT_DB;
+  }
+
+  const auto storage_path = StorageDir_(db_name);
+  if (!storage_path) return DeleteError::NON_EXISTENT;
+
+  {
+    auto db = db_handler_.Get(db_name);
+    if (!db) return DeleteError::NON_EXISTENT;
+    // TODO: ATM we assume REPLICA won't have streams,
+    //       this is a best effort approach just in case they do
+    //       there is still subtle data race we stream manipulation
+    //       can occur while we are dropping the database
+    db->prepare_for_deletion();
+    auto &database = *db->get();
+    database.streams()->StopAll();
+    database.streams()->DropAll();
+    database.thread_pool()->Shutdown();
+  }
+
+  // Remove from durability list
+  if (durability_) durability_->Delete(Durability::GenKey(db_name));
+
+  // Check if db exists
+  // Low level handlers
+  db_handler_.DeferDelete(db_name, [storage_path = *storage_path, db_name = std::string{db_name}]() {
+    // Delete disk storage
+    std::error_code ec;
+    (void)std::filesystem::remove_all(storage_path, ec);
+    if (ec) {
+      spdlog::error(R"(Failed to clean disk while deleting database "{}" stored in {})", db_name, storage_path);
+    }
+  });
+
+  return {};  // Success
+}
+
+void DbmsHandler::UpdateDurability(const storage::Config &config, std::optional<std::filesystem::path> rel_dir) {
+  if (!durability_) return;
+  // Save database in a list of active databases
+  const auto &key = Durability::GenKey(config.salient.name);
+  if (rel_dir == std::nullopt)
+    rel_dir =
+        std::filesystem::relative(config.durability.storage_directory, default_config_.durability.storage_directory);
+  const auto &val = Durability::GenVal(config.salient.uuid, *rel_dir);
+  durability_->Put(key, val);
+}
+
+AllSyncReplicaStatus DbmsHandler::Commit() {
+  if (system_transaction_ == std::nullopt || system_transaction_->delta == std::nullopt)
+    return AllSyncReplicaStatus::AllCommitsConfirmed;  // Nothing to commit
+  const auto &delta = *system_transaction_->delta;
+
+  auto sync_status = AllSyncReplicaStatus::AllCommitsConfirmed;
+  // TODO Create a system client that can handle all of this automatically
+  switch (delta.action) {
+    using enum SystemTransaction::Delta::Action;
+    case CREATE_DATABASE: {
+      // Replication
+      auto main_handler = [&](memgraph::replication::RoleMainData &main_data) {
+        // TODO: data race issue? registered_replicas_ access not protected
+        // This is sync in any case, as this is the startup
+        for (auto &client : main_data.registered_replicas_) {
+          bool completed = SteamAndFinalizeDelta<storage::replication::CreateDatabaseRpc>(
+              client,
+              [](const storage::replication::CreateDatabaseRes &response) {
+                return response.result != storage::replication::CreateDatabaseRes::Result::FAILURE;
+              },
+              std::string(main_data.epoch_.id()), last_commited_system_timestamp_,
+              system_transaction_->system_timestamp, delta.config);
+          // TODO: reduce duplicate code
+          if (!completed && client.mode_ == replication_coordination_glue::ReplicationMode::SYNC) {
+            sync_status = AllSyncReplicaStatus::SomeCommitsUnconfirmed;
+          }
+        }
+        // Sync database with REPLICAs
+        RecoverReplication(Get_(delta.config.name));
+      };
+      auto replica_handler = [](memgraph::replication::RoleReplicaData &) { /* Nothing to do */ };
+      std::visit(utils::Overloaded{main_handler, replica_handler}, repl_state_.ReplicationData());
+    } break;
+    case DROP_DATABASE: {
+      // Replication
+      auto main_handler = [&](memgraph::replication::RoleMainData &main_data) {
+        // TODO: data race issue? registered_replicas_ access not protected
+        // This is sync in any case, as this is the startup
+        for (auto &client : main_data.registered_replicas_) {
+          bool completed = SteamAndFinalizeDelta<storage::replication::DropDatabaseRpc>(
+              client,
+              [](const storage::replication::DropDatabaseRes &response) {
+                return response.result != storage::replication::DropDatabaseRes::Result::FAILURE;
+              },
+              std::string(main_data.epoch_.id()), last_commited_system_timestamp_,
+              system_transaction_->system_timestamp, delta.uuid);
+          // TODO: reduce duplicate code
+          if (!completed && client.mode_ == replication_coordination_glue::ReplicationMode::SYNC) {
+            sync_status = AllSyncReplicaStatus::SomeCommitsUnconfirmed;
+          }
+        }
+      };
+      auto replica_handler = [](memgraph::replication::RoleReplicaData &) { /* Nothing to do */ };
+      std::visit(utils::Overloaded{main_handler, replica_handler}, repl_state_.ReplicationData());
+    } break;
+  }
+
+  durability_->Put(kLastCommitedSystemTsKey, std::to_string(system_transaction_->system_timestamp));
+  last_commited_system_timestamp_ = system_transaction_->system_timestamp;
+  ResetSystemTransaction();
+  return sync_status;
+}
+
+#else  // not MG_ENTERPRISE
+
+AllSyncReplicaStatus DbmsHandler::Commit() {
+  if (system_transaction_ == std::nullopt || system_transaction_->delta == std::nullopt) {
+    return AllSyncReplicaStatus::AllCommitsConfirmed;  // Nothing to commit
+  }
+  const auto &delta = *system_transaction_->delta;
+
+  switch (delta.action) {
+    using enum SystemTransaction::Delta::Action;
+    case CREATE_DATABASE:
+    case DROP_DATABASE:
+      /* Community edition doesn't support multi-tenant replication */
+      break;
+  }
+
+  last_commited_system_timestamp_ = system_transaction_->system_timestamp;
+  ResetSystemTransaction();
+  return AllSyncReplicaStatus::AllCommitsConfirmed;
+}
+
+#endif
 }  // namespace memgraph::dbms

src/dbms/dbms_handler.hpp

@@ -12,34 +12,37 @@
 #pragma once
 
 #include <algorithm>
-#include <concepts>
+#include <atomic>
 #include <cstdint>
 #include <filesystem>
 #include <memory>
 #include <mutex>
 #include <optional>
-#include <ostream>
-#include <stdexcept>
 #include <system_error>
-#include <unordered_map>
+#include <utility>
 
 #include "auth/auth.hpp"
 #include "constants.hpp"
 #include "dbms/database.hpp"
 #include "dbms/inmemory/replication_handlers.hpp"
+#include "dbms/replication_handler.hpp"
+#include "kvstore/kvstore.hpp"
+#include "replication/replication_client.hpp"
+#include "storage/v2/config.hpp"
+#include "storage/v2/replication/enums.hpp"
+#include "storage/v2/replication/rpc.hpp"
+#include "storage/v2/transaction.hpp"
+#include "utils/thread_pool.hpp"
 #ifdef MG_ENTERPRISE
+#include "coordination/coordinator_state.hpp"
 #include "dbms/database_handler.hpp"
 #endif
-#include "dbms/replication_client.hpp"
+#include "dbms/transaction.hpp"
 #include "global.hpp"
 #include "query/config.hpp"
 #include "query/interpreter_context.hpp"
 #include "spdlog/spdlog.h"
-#include "storage/v2/durability/durability.hpp"
-#include "storage/v2/durability/paths.hpp"
 #include "storage/v2/isolation_level.hpp"
-#include "utils/exceptions.hpp"
-#include "utils/file.hpp"
 #include "utils/logging.hpp"
 #include "utils/result.hpp"
 #include "utils/rw_lock.hpp"
@@ -48,6 +51,11 @@
 
 namespace memgraph::dbms {
 
+enum class AllSyncReplicaStatus {
+  AllCommitsConfirmed,
+  SomeCommitsUnconfirmed,
+};
+
 struct Statistics {
   uint64_t num_vertex;           //!< Sum of vertexes in every database
   uint64_t num_edges;            //!< Sum of edges in every database
@@ -102,11 +110,10 @@ class DbmsHandler {
    * @param configs storage configuration
    * @param auth pointer to the global authenticator
    * @param recovery_on_startup restore databases (and its content) and authentication data
-   * @param delete_on_drop when dropping delete any associated directories on disk
    */
   DbmsHandler(storage::Config config,
               memgraph::utils::Synchronized<memgraph::auth::Auth, memgraph::utils::WritePrioritizedRWLock> *auth,
-              bool recovery_on_startup, bool delete_on_drop);  // TODO If more arguments are added use a config strut
+              bool recovery_on_startup);  // TODO If more arguments are added use a config struct
 #else
   /**
    * @brief Initialize the handler. A single database is supported in community edition.
@@ -116,10 +123,12 @@ class DbmsHandler {
   DbmsHandler(storage::Config config)
       : repl_state_{ReplicationStateRootPath(config)},
         db_gatekeeper_{[&] {
-                         config.name = kDefaultDB;
+                         config.salient.name = kDefaultDB;
                          return std::move(config);
                        }(),
-                       repl_state_} {}
+                       repl_state_} {
+    RecoverReplication(Get());
+  }
 #endif
 
 #ifdef MG_ENTERPRISE
@@ -131,9 +140,56 @@ class DbmsHandler {
    */
   NewResultT New(const std::string &name) {
     std::lock_guard<LockT> wr(lock_);
-    return New_(name, name);
+    const auto uuid = utils::UUID{};
+    return New_(name, uuid);
   }
 
+  /**
+   * @brief Create new if name/uuid do not match any database. Drop and recreate if database already present.
+   * @note Default database is not dropped, only its UUID is updated and only if the database is clean.
+   *
+   * @param config desired salient config
+   * @return NewResultT context on success, error on failure
+   */
+  NewResultT Update(const storage::SalientConfig &config) {
+    std::lock_guard<LockT> wr(lock_);
+    auto new_db = New_(config);
+    if (new_db.HasValue() || new_db.GetError() != NewError::EXISTS) {
+      // NOTE: If db already exists we retry below
+      return new_db;
+    }
+
+    spdlog::debug("Trying to create db '{}' on replica which already exists.", config.name);
+
+    auto db = Get_(config.name);
+    if (db->uuid() == config.uuid) {  // Same db
+      return db;
+    }
+
+    spdlog::debug("Different UUIDs");
+
+    // TODO: Fix this hack
+    if (config.name == kDefaultDB) {
+      if (db->storage()->repl_storage_state_.last_commit_timestamp_ != storage::kTimestampInitialId) {
+        spdlog::debug("Default storage is not clean, cannot update UUID...");
+        return NewError::GENERIC;  // Update error
+      }
+      spdlog::debug("Update default db's UUID");
+      // Default db cannot be deleted and remade, have to just update the UUID
+      db->storage()->config_.salient.uuid = config.uuid;
+      UpdateDurability(db->storage()->config_, ".");
+      return db;
+    }
+
+    spdlog::debug("Drop database and recreate with the correct UUID");
+    // Defer drop
+    (void)Delete_(db->name());
+    // Second attempt
+    return New_(config);
+  }
+
+  void UpdateDurability(const storage::Config &config, std::optional<std::filesystem::path> rel_dir = {});
+
   /**
    * @brief Get the context associated with the "name" database
    *
@@ -145,6 +201,19 @@ class DbmsHandler {
     std::shared_lock<LockT> rd(lock_);
     return Get_(name);
   }
+
+  /**
+   * @brief Get the context associated with the UUID database
+   *
+   * @param uuid
+   * @return DatabaseAccess
+   * @throw UnknownDatabaseException if database not found
+   */
+  DatabaseAccess Get(const utils::UUID &uuid) {
+    std::shared_lock<LockT> rd(lock_);
+    return Get_(uuid);
+  }
+
 #else
   /**
    * @brief Get the context associated with the default database
@@ -160,50 +229,28 @@ class DbmsHandler {
 
 #ifdef MG_ENTERPRISE
   /**
-   * @brief Delete database.
+   * @brief Attempt to delete database.
    *
    * @param db_name database name
    * @return DeleteResult error on failure
    */
-  DeleteResult Delete(const std::string &db_name) {
-    std::lock_guard<LockT> wr(lock_);
-    if (db_name == kDefaultDB) {
-      // MSG cannot delete the default db
-      return DeleteError::DEFAULT_DB;
-    }
+  DeleteResult TryDelete(std::string_view db_name);
 
-    const auto storage_path = StorageDir_(db_name);
-    if (!storage_path) return DeleteError::NON_EXISTENT;
+  /**
+   * @brief Delete or defer deletion of database.
+   *
+   * @param db_name database name
+   * @return DeleteResult error on failure
+   */
+  DeleteResult Delete(std::string_view db_name);
 
-    // Check if db exists
-    try {
-      // Low level handlers
-      if (!db_handler_.Delete(db_name)) {
-        return DeleteError::USING;
-      }
-    } catch (utils::BasicException &) {
-      return DeleteError::NON_EXISTENT;
-    }
-
-    // Remove from durability list
-    if (durability_) durability_->Delete(db_name);
-
-    // Delete disk storage
-    if (delete_on_drop_) {
-      std::error_code ec;
-      (void)std::filesystem::remove_all(*storage_path, ec);
-      if (ec) {
-        spdlog::error("Failed to clean disk while deleting database \"{}\".", db_name);
-        defunct_dbs_.emplace(db_name);
-        return DeleteError::DISK_FAIL;
-      }
-    }
-
-    // Delete from defunct_dbs_ (in case a second delete call was successful)
-    defunct_dbs_.erase(db_name);
-
-    return {};  // Success
-  }
+  /**
+   * @brief Delete or defer deletion of database.
+   *
+   * @param uuid database UUID
+   * @return DeleteResult error on failure
+   */
+  DeleteResult Delete(utils::UUID uuid);
 #endif
 
   /**
@@ -216,7 +263,7 @@ class DbmsHandler {
     std::shared_lock<LockT> rd(lock_);
     return db_handler_.All();
 #else
-    return {db_gatekeeper_.access()->get()->id()};
+    return {db_gatekeeper_.access()->get()->name()};
 #endif
   }
 
@@ -226,6 +273,10 @@ class DbmsHandler {
   bool IsMain() const { return repl_state_.IsMain(); }
   bool IsReplica() const { return repl_state_.IsReplica(); }
 
+#ifdef MG_ENTERPRISE
+  coordination::CoordinatorState &CoordinatorState() { return coordinator_state_; }
+#endif
+
   /**
    * @brief Return the statistics all databases.
    *
@@ -305,7 +356,7 @@ class DbmsHandler {
       auto db_acc_opt = db_gk.access();
       if (db_acc_opt) {
         auto &db_acc = *db_acc_opt;
-        spdlog::debug("Restoring trigger for database \"{}\"", db_acc->id());
+        spdlog::debug("Restoring trigger for database \"{}\"", db_acc->name());
         auto storage_accessor = db_acc->Access();
         auto dba = memgraph::query::DbAccessor{storage_accessor.get()};
         db_acc->trigger_store()->RestoreTriggers(&ic->ast_cache, &dba, ic->config.query, ic->auth_checker);
@@ -330,7 +381,7 @@ class DbmsHandler {
       auto db_acc = db_gk.access();
       if (db_acc) {
         auto *db = db_acc->get();
-        spdlog::debug("Restoring streams for database \"{}\"", db->id());
+        spdlog::debug("Restoring streams for database \"{}\"", db->name());
         db->streams()->RestoreStreams(*db_acc, ic);
       }
     }
@@ -341,7 +392,7 @@ class DbmsHandler {
    *
    * @param f
    */
-  void ForEach(auto f) {
+  void ForEach(std::invocable<DatabaseAccess> auto f) {
 #ifdef MG_ENTERPRISE
     std::shared_lock<LockT> rd(lock_);
     for (auto &[_, db_gk] : db_handler_) {
@@ -351,33 +402,103 @@ class DbmsHandler {
 #endif
       auto db_acc = db_gk.access();
       if (db_acc) {  // This isn't an error, just a defunct db
-        f(db_acc->get());
+        f(*db_acc);
       }
     }
   }
 
-  /**
-   * @brief todo
-   *
-   * @param f
-   */
-  void ForOne(auto f) {
+  void NewSystemTransaction() {
+    DMG_ASSERT(!system_transaction_, "Already running a system transaction");
+    system_transaction_.emplace(++system_timestamp_);
+  }
+
+  void ResetSystemTransaction() { system_transaction_.reset(); }
+
+  //! \tparam RPC An rpc::RequestResponse
+  //! \tparam Args the args type
+  //! \param client the client to use for rpc communication
+  //! \param check predicate to check response is ok
+  //! \param args arguments to forward to the rpc request
+  //! \return If replica stream is completed or enqueued
+  template <typename RPC, typename... Args>
+  bool SteamAndFinalizeDelta(auto &client, auto &&check, Args &&...args) {
+    try {
+      auto stream = client.rpc_client_.template Stream<RPC>(std::forward<Args>(args)...);
+      auto task = [&client, check = std::forward<decltype(check)>(check), stream = std::move(stream)]() mutable {
+        if (stream.IsDefunct()) {
+          client.state_.WithLock([](auto &state) { state = memgraph::replication::ReplicationClient::State::BEHIND; });
+          return false;
+        }
+        try {
+          if (check(stream.AwaitResponse())) {
+            return true;
+          }
+        } catch (memgraph::rpc::GenericRpcFailedException const &e) {
+          // swallow error, fallthrough to error handling
+        }
+        // This replica needs SYSTEM recovery
+        client.state_.WithLock([](auto &state) { state = memgraph::replication::ReplicationClient::State::BEHIND; });
+        return false;
+      };
+
+      if (client.mode_ == memgraph::replication_coordination_glue::ReplicationMode::ASYNC) {
+        client.thread_pool_.AddTask([task = utils::CopyMovableFunctionWrapper{std::move(task)}]() mutable { task(); });
+        return true;
+      }
+
+      return task();
+    } catch (memgraph::rpc::GenericRpcFailedException const &e) {
+      // This replica needs SYSTEM recovery
+      client.state_.WithLock([](auto &state) { state = memgraph::replication::ReplicationClient::State::BEHIND; });
+      return false;
+    }
+  };
+
+  AllSyncReplicaStatus Commit();
+
+  auto LastCommitedTS() const -> uint64_t { return last_commited_system_timestamp_; }
+  void SetLastCommitedTS(uint64_t new_ts) { last_commited_system_timestamp_.store(new_ts); }
+
 #ifdef MG_ENTERPRISE
-    std::shared_lock<LockT> rd(lock_);
-    for (auto &[_, db_gk] : db_handler_) {
-      auto db_acc = db_gk.access();
-      if (db_acc) {                   // This isn't an error, just a defunct db
-        if (f(db_acc->get())) break;  // Run until the first successful one
+  // When being called by intepreter no need to gain lock, it should already be under a system transaction
+  // But concurrently the FrequentCheck is running and will need to lock before reading last_commited_system_timestamp_
+  template <bool REQUIRE_LOCK = false>
+  void SystemRestore(replication::ReplicationClient &client) {
+    // Check if system is up to date
+    if (client.state_.WithLock(
+            [](auto &state) { return state == memgraph::replication::ReplicationClient::State::READY; }))
+      return;
+
+    // Try to recover...
+    {
+      auto [database_configs, last_commited_system_timestamp] = std::invoke([&] {
+        auto sys_guard =
+            std::unique_lock{system_lock_, std::defer_lock};  // ensure no other system transaction in progress
+        if constexpr (REQUIRE_LOCK) {
+          sys_guard.lock();
+        }
+        auto configs = std::vector<storage::SalientConfig>{};
+        ForEach([&configs](DatabaseAccess acc) { configs.emplace_back(acc->config().salient); });
+        return std::pair{configs, last_commited_system_timestamp_.load()};
+      });
+      try {
+        auto stream = client.rpc_client_.Stream<storage::replication::SystemRecoveryRpc>(last_commited_system_timestamp,
+                                                                                         std::move(database_configs));
+        const auto response = stream.AwaitResponse();
+        if (response.result == storage::replication::SystemRecoveryRes::Result::FAILURE) {
+          client.state_.WithLock([](auto &state) { state = memgraph::replication::ReplicationClient::State::BEHIND; });
+          return;
+        }
+      } catch (memgraph::rpc::GenericRpcFailedException const &e) {
+        client.state_.WithLock([](auto &state) { state = memgraph::replication::ReplicationClient::State::BEHIND; });
+        return;
       }
     }
-#else
-    {
-      auto db_acc = db_gatekeeper_.access();
-      MG_ASSERT(db_acc, "Should always have the database");
-      f(db_acc->get());
-    }
-#endif
+
+    // Successfully recovered
+    client.state_.WithLock([](auto &state) { state = memgraph::replication::ReplicationClient::State::READY; });
   }
+#endif
 
  private:
 #ifdef MG_ENTERPRISE
@@ -387,7 +508,7 @@ class DbmsHandler {
    * @param name Database name
    * @return std::optional<std::filesystem::path>
    */
-  std::optional<std::filesystem::path> StorageDir_(const std::string &name) {
+  std::optional<std::filesystem::path> StorageDir_(std::string_view name) {
     const auto conf = db_handler_.GetConfig(name);
     if (conf) {
       return conf->durability.storage_directory;
@@ -400,105 +521,108 @@ class DbmsHandler {
    * @brief Create a new Database associated with the "name" database
    *
    * @param name name of the database
+   * @param uuid undelying RocksDB directory
    * @return NewResultT context on success, error on failure
    */
-  NewResultT New_(const std::string &name) { return New_(name, name); }
+  NewResultT New_(std::string_view name, utils::UUID uuid, std::optional<std::filesystem::path> rel_dir = {}) {
+    auto config_copy = default_config_;
+    config_copy.salient.name = name;
+    config_copy.salient.uuid = uuid;
+    spdlog::debug("Creating database '{}' - '{}'", name, std::string{uuid});
+    if (rel_dir) {
+      storage::UpdatePaths(config_copy, default_config_.durability.storage_directory / *rel_dir);
+    } else {
+      storage::UpdatePaths(config_copy,
+                           default_config_.durability.storage_directory / kMultiTenantDir / std::string{uuid});
+    }
+    return New_(std::move(config_copy));
+  }
 
   /**
-   * @brief Create a new Database associated with the "name" database
+   * @brief Create a new Database using the passed configuration
    *
-   * @param name name of the database
-   * @param storage_subdir undelying RocksDB directory
+   * @param config configuration to be used
    * @return NewResultT context on success, error on failure
    */
-  NewResultT New_(const std::string &name, std::filesystem::path storage_subdir) {
+  NewResultT New_(const storage::SalientConfig &config) {
     auto config_copy = default_config_;
-    storage::UpdatePaths(config_copy, default_config_.durability.storage_directory / storage_subdir);
-    return New_(name, config_copy);
+    config_copy.salient = config;  // name, uuid, mode, etc
+    UpdatePaths(config_copy, config_copy.durability.storage_directory / kMultiTenantDir / std::string{config.uuid});
+    return New_(std::move(config_copy));
   }
 
   /**
    * @brief Create a new Database associated with the "name" database
    *
-   * @param name name of the database
    * @param storage_config storage configuration
    * @return NewResultT context on success, error on failure
    */
-  NewResultT New_(const std::string &name, storage::Config &storage_config) {
-    if (defunct_dbs_.contains(name)) {
-      spdlog::warn("Failed to generate database due to the unknown state of the previously defunct database \"{}\".",
-                   name);
-      return NewError::DEFUNCT;
-    }
+  NewResultT New_(storage::Config storage_config);
 
-    auto new_db = db_handler_.New(name, storage_config, repl_state_);
-    if (new_db.HasValue()) {
-      // Success
-      if (durability_) durability_->Put(name, "ok");  // TODO: Serialize the configuration?
-      return new_db.GetValue();
-    }
-    return new_db.GetError();
-  }
+  // TODO: new overload of Delete_ with DatabaseAccess
+  DeleteResult Delete_(std::string_view db_name);
 
   /**
    * @brief Create a new Database associated with the default database
    *
    * @return NewResultT context on success, error on failure
    */
-  NewResultT NewDefault_() {
-    // Create the default DB in the root (this is how it was done pre multi-tenancy)
-    auto res = New_(kDefaultDB, "..");
-    if (res.HasValue()) {
-      // For back-compatibility...
-      // Recreate the dbms layout for the default db and symlink to the root
-      const auto dir = StorageDir_(kDefaultDB);
-      MG_ASSERT(dir, "Failed to find storage path.");
-      const auto main_dir = *dir / "databases" / kDefaultDB;
+  void SetupDefault_() {
+    try {
+      Get(kDefaultDB);
+    } catch (const UnknownDatabaseException &) {
+      // No default DB restored, create it
+      MG_ASSERT(New_(kDefaultDB, {/* random UUID */}, ".").HasValue(), "Failed while creating the default database");
+    }
 
-      if (!std::filesystem::exists(main_dir)) {
-        std::filesystem::create_directory(main_dir);
-      }
+    // For back-compatibility...
+    // Recreate the dbms layout for the default db and symlink to the root
+    const auto dir = StorageDir_(kDefaultDB);
+    MG_ASSERT(dir, "Failed to find storage path.");
+    const auto main_dir = *dir / kMultiTenantDir / kDefaultDB;
 
-      // Force link on-disk directories
-      const auto conf = db_handler_.GetConfig(kDefaultDB);
-      MG_ASSERT(conf, "No configuration for the default database.");
-      const auto &tmp_conf = conf->disk;
-      std::vector<std::filesystem::path> to_link{
-          tmp_conf.main_storage_directory,         tmp_conf.label_index_directory,
-          tmp_conf.label_property_index_directory, tmp_conf.unique_constraints_directory,
-          tmp_conf.name_id_mapper_directory,       tmp_conf.id_name_mapper_directory,
-          tmp_conf.durability_directory,           tmp_conf.wal_directory,
-      };
+    if (!std::filesystem::exists(main_dir)) {
+      std::filesystem::create_directory(main_dir);
+    }
 
-      // Add in-memory paths
-      // Some directories are redundant (skip those)
-      const std::vector<std::string> skip{".lock", "audit_log", "auth", "databases", "internal_modules", "settings"};
-      for (auto const &item : std::filesystem::directory_iterator{*dir}) {
-        const auto dir_name = std::filesystem::relative(item.path(), item.path().parent_path());
-        if (std::find(skip.begin(), skip.end(), dir_name) != skip.end()) continue;
-        to_link.push_back(item.path());
-      }
+    // Force link on-disk directories
+    const auto conf = db_handler_.GetConfig(kDefaultDB);
+    MG_ASSERT(conf, "No configuration for the default database.");
+    const auto &tmp_conf = conf->disk;
+    std::vector<std::filesystem::path> to_link{
+        tmp_conf.main_storage_directory,         tmp_conf.label_index_directory,
+        tmp_conf.label_property_index_directory, tmp_conf.unique_constraints_directory,
+        tmp_conf.name_id_mapper_directory,       tmp_conf.id_name_mapper_directory,
+        tmp_conf.durability_directory,           tmp_conf.wal_directory,
+    };
 
-      // Symlink to root dir
-      for (auto const &item : to_link) {
-        const auto dir_name = std::filesystem::relative(item, item.parent_path());
-        const auto link = main_dir / dir_name;
-        const auto to = std::filesystem::relative(item, main_dir);
-        if (!std::filesystem::is_symlink(link) && !std::filesystem::exists(link)) {
-          std::filesystem::create_directory_symlink(to, link);
-        } else {  // Check existing link
-          std::error_code ec;
-          const auto test_link = std::filesystem::read_symlink(link, ec);
-          if (ec || test_link != to) {
-            MG_ASSERT(false,
-                      "Memgraph storage directory incompatible with new version.\n"
-                      "Please use a clean directory or remove \"{}\" and try again.",
-                      link.string());
-          }
+    // Add in-memory paths
+    // Some directories are redundant (skip those)
+    const std::vector<std::string> skip{".lock", "audit_log", "auth", "databases", "internal_modules", "settings"};
+    for (auto const &item : std::filesystem::directory_iterator{*dir}) {
+      const auto dir_name = std::filesystem::relative(item.path(), item.path().parent_path());
+      if (std::find(skip.begin(), skip.end(), dir_name) != skip.end()) continue;
+      to_link.push_back(item.path());
+    }
+
+    // Symlink to root dir
+    for (auto const &item : to_link) {
+      const auto dir_name = std::filesystem::relative(item, item.parent_path());
+      const auto link = main_dir / dir_name;
+      const auto to = std::filesystem::relative(item, main_dir);
+      if (!std::filesystem::is_symlink(link) && !std::filesystem::exists(link)) {
+        std::filesystem::create_directory_symlink(to, link);
+      } else {  // Check existing link
+        std::error_code ec;
+        const auto test_link = std::filesystem::read_symlink(link, ec);
+        if (ec || test_link != to) {
+          MG_ASSERT(false,
+                    "Memgraph storage directory incompatible with new version.\n"
+                    "Please use a clean directory or remove \"{}\" and try again.",
+                    link.string());
         }
       }
     }
-    return res;
   }
 
   /**
@@ -516,17 +640,57 @@ class DbmsHandler {
     throw UnknownDatabaseException("Tried to retrieve an unknown database \"{}\".", name);
   }
 
+  /**
+   * @brief Get the context associated with the UUID database
+   *
+   * @param uuid
+   * @return DatabaseAccess
+   * @throw UnknownDatabaseException if database not found
+   */
+  DatabaseAccess Get_(const utils::UUID &uuid) {
+    // TODO Speed up
+    for (auto &[_, db_gk] : db_handler_) {
+      auto acc = db_gk.access();
+      if (acc->get()->uuid() == uuid) {
+        return std::move(*acc);
+      }
+    }
+    throw UnknownDatabaseException("Tried to retrieve an unknown database with UUID \"{}\".", std::string{uuid});
+  }
+#endif
+
+  void RecoverReplication(DatabaseAccess db_acc) {
+    if (allow_mt_repl || db_acc->name() == dbms::kDefaultDB) {
+      // Handle global replication state
+      spdlog::info("Replication configuration will be stored and will be automatically restored in case of a crash.");
+      // RECOVER REPLICA CONNECTIONS
+      memgraph::dbms::RestoreReplication(repl_state_, std::move(db_acc));
+    } else if (const ::memgraph::replication::RoleMainData *data =
+                   std::get_if<::memgraph::replication::RoleMainData>(&repl_state_.ReplicationData());
+               data && !data->registered_replicas_.empty()) {
+      spdlog::warn("Multi-tenant replication is currently not supported!");
+    }
+  }
+
+#ifdef MG_ENTERPRISE
   mutable LockT lock_{utils::RWLock::Priority::READ};  //!< protective lock
   storage::Config default_config_;                     //!< Storage configuration used when creating new databases
   DatabaseHandler db_handler_;                         //!< multi-tenancy storage handler
   std::unique_ptr<kvstore::KVStore> durability_;       //!< list of active dbs (pointer so we can postpone its creation)
-  bool delete_on_drop_;                                //!< Flag defining if dropping storage also deletes its directory
-  std::set<std::string> defunct_dbs_;  //!< Databases that are in an unknown state due to various failures
+  coordination::CoordinatorState coordinator_state_;  //!< Replication coordinator
 #endif
+  // TODO: Make an api
+ public:
+  utils::ResourceLock system_lock_{};  //!> Ensure exclusive access for system queries
+ private:
+  std::optional<SystemTransaction> system_transaction_;      //!< Current system transaction (only one at a time)
+  uint64_t system_timestamp_{storage::kTimestampInitialId};  //!< System timestamp
+  std::atomic_uint64_t last_commited_system_timestamp_{
+      storage::kTimestampInitialId};          //!< Last commited system timestamp
   replication::ReplicationState repl_state_;  //!< Global replication state
 #ifndef MG_ENTERPRISE
   mutable utils::Gatekeeper<Database> db_gatekeeper_;  //!< Single databases gatekeeper
 #endif
-};
+};  // namespace memgraph::dbms
 
 }  // namespace memgraph::dbms

src/dbms/handler.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -21,6 +21,7 @@
 #include "utils/exceptions.hpp"
 #include "utils/gatekeeper.hpp"
 #include "utils/result.hpp"
+#include "utils/thread_pool.hpp"
 
 namespace memgraph::dbms {
 
@@ -82,7 +83,7 @@ class Handler {
    * @return true on success
    * @throw BasicException
    */
-  bool Delete(const std::string &name) {
+  bool TryDelete(std::string_view name) {
     if (auto itr = items_.find(name); itr != items_.end()) {
       auto db_acc = itr->second.access();
       if (db_acc && db_acc->try_delete()) {
@@ -92,9 +93,42 @@ class Handler {
       }
       return false;
     }
+    // TODO: Change to return enum
     throw utils::BasicException("Unknown item \"{}\".", name);
   }
 
+  /**
+   * @brief Delete or defunct the context associated with the name.
+   *
+   * @param name Name associated with the context to delete
+   * @param post_delete_func What to do after deletion has happened
+   */
+  template <typename Func>
+  void DeferDelete(std::string_view name, Func &&post_delete_func) {
+    auto itr = items_.find(name);
+    if (itr == items_.end()) return;
+
+    auto db_acc = itr->second.access();
+    if (!db_acc) return;
+
+    if (db_acc->try_delete()) {
+      // Delete the database now
+      db_acc->reset();
+      post_delete_func();
+    } else {
+      // Defer deletion
+      db_acc->reset();
+      // TODO: Make sure this shuts down correctly
+      auto task = [gk = std::move(itr->second), post_delete_func = std::forward<Func>(post_delete_func)]() mutable {
+        gk.~Gatekeeper<T>();
+        post_delete_func();
+      };
+      defer_pool_.AddTask(utils::CopyMovableFunctionWrapper{std::move(task)});
+    }
+    // In any case remove from handled map
+    items_.erase(itr);
+  }
+
   /**
    * @brief Check if a name is already used.
    *
@@ -120,6 +154,7 @@ class Handler {
  private:
   std::unordered_map<std::string, utils::Gatekeeper<T>, string_hash, std::equal_to<>>
       items_;  //!< map to all active items
+  utils::ThreadPool defer_pool_{1};
 };
 
 }  // namespace memgraph::dbms

src/dbms/inmemory/replication_handlers.cpp

@@ -10,6 +10,7 @@
 // licenses/APL.txt.
 
 #include "dbms/inmemory/replication_handlers.hpp"
+#include <chrono>
 #include <optional>
 #include "dbms/constants.hpp"
 #include "dbms/dbms_handler.hpp"
@@ -22,7 +23,7 @@
 #include "storage/v2/inmemory/storage.hpp"
 #include "storage/v2/inmemory/unique_constraints.hpp"
 
-using memgraph::replication::ReplicationRole;
+using memgraph::replication_coordination_glue::ReplicationRole;
 using memgraph::storage::Delta;
 using memgraph::storage::EdgeAccessor;
 using memgraph::storage::EdgeRef;
@@ -49,29 +50,29 @@ std::pair<uint64_t, WalDeltaData> ReadDelta(storage::durability::BaseDecoder *de
   }
 };
 
-std::optional<DatabaseAccess> GetDatabaseAccessor(dbms::DbmsHandler *dbms_handler, std::string_view db_name) {
+std::optional<DatabaseAccess> GetDatabaseAccessor(dbms::DbmsHandler *dbms_handler, const utils::UUID &uuid) {
   try {
 #ifdef MG_ENTERPRISE
-    auto acc = dbms_handler->Get(db_name);
-#else
-    if (db_name != dbms::kDefaultDB) {
-      spdlog::warn("Trying to replicate a non-default database on a community replica.");
-      return std::nullopt;
-    }
-    auto acc = dbms_handler->Get();
-#endif
+    auto acc = dbms_handler->Get(uuid);
     if (!acc) {
-      spdlog::error("Failed to get access to ", db_name);
+      spdlog::error("Failed to get access to UUID ", std::string{uuid});
       return std::nullopt;
     }
+#else
+    auto acc = dbms_handler->Get();
+    if (!acc) {
+      spdlog::warn("Failed to get access to the default db.");
+      return std::nullopt;
+    }
+#endif
     auto *inmem_storage = dynamic_cast<storage::InMemoryStorage *>(acc.get()->storage());
     if (!inmem_storage || inmem_storage->storage_mode_ != storage::StorageMode::IN_MEMORY_TRANSACTIONAL) {
-      spdlog::error("Database \"{}\" is not IN_MEMORY_TRANSACTIONAL.", db_name);
+      spdlog::error("Database is not IN_MEMORY_TRANSACTIONAL.");
       return std::nullopt;
     }
     return std::optional{std::move(acc)};
   } catch (const dbms::UnknownDatabaseException &e) {
-    spdlog::warn("No database \"{}\" on replica!", db_name);
+    spdlog::warn("No database with UUID \"{}\" on replica!", std::string{uuid});
     return std::nullopt;
   }
 }
@@ -109,13 +110,16 @@ void InMemoryReplicationHandlers::HeartbeatHandler(dbms::DbmsHandler *dbms_handl
                                                    slk::Builder *res_builder) {
   storage::replication::HeartbeatReq req;
   slk::Load(&req, req_reader);
-  auto const db_acc = GetDatabaseAccessor(dbms_handler, req.db_name);
-  if (!db_acc) return;
+  auto const db_acc = GetDatabaseAccessor(dbms_handler, req.uuid);
+  if (!db_acc) {
+    storage::replication::HeartbeatRes res{false, 0, ""};
+    slk::Save(res, res_builder);
+    return;
+  }
 
   // TODO: this handler is agnostic of InMemory, move to be reused by on-disk
   auto const *storage = db_acc->get()->storage();
-  storage::replication::HeartbeatRes res{storage->id(), true,
-                                         storage->repl_storage_state_.last_commit_timestamp_.load(),
+  storage::replication::HeartbeatRes res{true, storage->repl_storage_state_.last_commit_timestamp_.load(),
                                          std::string{storage->repl_storage_state_.epoch_.id()}};
   slk::Save(res, res_builder);
 }
@@ -124,8 +128,12 @@ void InMemoryReplicationHandlers::AppendDeltasHandler(dbms::DbmsHandler *dbms_ha
                                                       slk::Builder *res_builder) {
   storage::replication::AppendDeltasReq req;
   slk::Load(&req, req_reader);
-  auto db_acc = GetDatabaseAccessor(dbms_handler, req.db_name);
-  if (!db_acc) return;
+  auto db_acc = GetDatabaseAccessor(dbms_handler, req.uuid);
+  if (!db_acc) {
+    storage::replication::AppendDeltasRes res{false, 0};
+    slk::Save(res, res_builder);
+    return;
+  }
 
   storage::replication::Decoder decoder(req_reader);
 
@@ -165,7 +173,7 @@ void InMemoryReplicationHandlers::AppendDeltasHandler(dbms::DbmsHandler *dbms_ha
           storage::durability::kVersion);  // TODO: Check if we are always using the latest version when replicating
     }
 
-    storage::replication::AppendDeltasRes res{storage->id(), false, repl_storage_state.last_commit_timestamp_.load()};
+    storage::replication::AppendDeltasRes res{false, repl_storage_state.last_commit_timestamp_.load()};
     slk::Save(res, res_builder);
     return;
   }
@@ -174,7 +182,7 @@ void InMemoryReplicationHandlers::AppendDeltasHandler(dbms::DbmsHandler *dbms_ha
       storage, &decoder,
       storage::durability::kVersion);  // TODO: Check if we are always using the latest version when replicating
 
-  storage::replication::AppendDeltasRes res{storage->id(), true, repl_storage_state.last_commit_timestamp_.load()};
+  storage::replication::AppendDeltasRes res{true, repl_storage_state.last_commit_timestamp_.load()};
   slk::Save(res, res_builder);
   spdlog::debug("Replication recovery from append deltas finished, replica is now up to date!");
 }
@@ -183,8 +191,12 @@ void InMemoryReplicationHandlers::SnapshotHandler(dbms::DbmsHandler *dbms_handle
                                                   slk::Builder *res_builder) {
   storage::replication::SnapshotReq req;
   slk::Load(&req, req_reader);
-  auto db_acc = GetDatabaseAccessor(dbms_handler, req.db_name);
-  if (!db_acc) return;
+  auto db_acc = GetDatabaseAccessor(dbms_handler, req.uuid);
+  if (!db_acc) {
+    storage::replication::SnapshotRes res{false, 0};
+    slk::Save(res, res_builder);
+    return;
+  }
 
   storage::replication::Decoder decoder(req_reader);
 
@@ -232,8 +244,7 @@ void InMemoryReplicationHandlers::SnapshotHandler(dbms::DbmsHandler *dbms_handle
   }
   storage_guard.unlock();
 
-  storage::replication::SnapshotRes res{storage->id(), true,
-                                        storage->repl_storage_state_.last_commit_timestamp_.load()};
+  storage::replication::SnapshotRes res{true, storage->repl_storage_state_.last_commit_timestamp_.load()};
   slk::Save(res, res_builder);
 
   spdlog::trace("Deleting old snapshot files due to snapshot recovery.");
@@ -263,8 +274,12 @@ void InMemoryReplicationHandlers::WalFilesHandler(dbms::DbmsHandler *dbms_handle
                                                   slk::Builder *res_builder) {
   storage::replication::WalFilesReq req;
   slk::Load(&req, req_reader);
-  auto db_acc = GetDatabaseAccessor(dbms_handler, req.db_name);
-  if (!db_acc) return;
+  auto db_acc = GetDatabaseAccessor(dbms_handler, req.uuid);
+  if (!db_acc) {
+    storage::replication::WalFilesRes res{false, 0};
+    slk::Save(res, res_builder);
+    return;
+  }
 
   const auto wal_file_number = req.file_number;
   spdlog::debug("Received WAL files: {}", wal_file_number);
@@ -278,8 +293,7 @@ void InMemoryReplicationHandlers::WalFilesHandler(dbms::DbmsHandler *dbms_handle
     LoadWal(storage, &decoder);
   }
 
-  storage::replication::WalFilesRes res{storage->id(), true,
-                                        storage->repl_storage_state_.last_commit_timestamp_.load()};
+  storage::replication::WalFilesRes res{true, storage->repl_storage_state_.last_commit_timestamp_.load()};
   slk::Save(res, res_builder);
   spdlog::debug("Replication recovery from WAL files ended successfully, replica is now up to date!");
 }
@@ -288,8 +302,12 @@ void InMemoryReplicationHandlers::CurrentWalHandler(dbms::DbmsHandler *dbms_hand
                                                     slk::Builder *res_builder) {
   storage::replication::CurrentWalReq req;
   slk::Load(&req, req_reader);
-  auto db_acc = GetDatabaseAccessor(dbms_handler, req.db_name);
-  if (!db_acc) return;
+  auto db_acc = GetDatabaseAccessor(dbms_handler, req.uuid);
+  if (!db_acc) {
+    storage::replication::CurrentWalRes res{false, 0};
+    slk::Save(res, res_builder);
+    return;
+  }
 
   storage::replication::Decoder decoder(req_reader);
 
@@ -298,8 +316,7 @@ void InMemoryReplicationHandlers::CurrentWalHandler(dbms::DbmsHandler *dbms_hand
 
   LoadWal(storage, &decoder);
 
-  storage::replication::CurrentWalRes res{storage->id(), true,
-                                          storage->repl_storage_state_.last_commit_timestamp_.load()};
+  storage::replication::CurrentWalRes res{true, storage->repl_storage_state_.last_commit_timestamp_.load()};
   slk::Save(res, res_builder);
   spdlog::debug("Replication recovery from current WAL ended successfully, replica is now up to date!");
 }
@@ -318,6 +335,8 @@ void InMemoryReplicationHandlers::LoadWal(storage::InMemoryStorage *storage, sto
     }
     auto &replica_epoch = storage->repl_storage_state_.epoch_;
     if (wal_info.epoch_id != replica_epoch.id()) {
+      // questionable behaviour, we trust that any change in epoch implies change in who is MAIN
+      // when we use high availability, this assumption need to be checked.
       auto prev_epoch = replica_epoch.SetEpoch(wal_info.epoch_id);
       storage->repl_storage_state_.AddEpochToHistoryForce(prev_epoch);
     }
@@ -355,13 +374,16 @@ void InMemoryReplicationHandlers::TimestampHandler(dbms::DbmsHandler *dbms_handl
                                                    slk::Builder *res_builder) {
   storage::replication::TimestampReq req;
   slk::Load(&req, req_reader);
-  auto const db_acc = GetDatabaseAccessor(dbms_handler, req.db_name);
-  if (!db_acc) return;
+  auto const db_acc = GetDatabaseAccessor(dbms_handler, req.uuid);
+  if (!db_acc) {
+    storage::replication::TimestampRes res{false, 0};
+    slk::Save(res, res_builder);
+    return;
+  }
 
   // TODO: this handler is agnostic of InMemory, move to be reused by on-disk
   auto const *storage = db_acc->get()->storage();
-  storage::replication::TimestampRes res{storage->id(), true,
-                                         storage->repl_storage_state_.last_commit_timestamp_.load()};
+  storage::replication::TimestampRes res{true, storage->repl_storage_state_.last_commit_timestamp_.load()};
   slk::Save(res, res_builder);
 }
 
@@ -505,7 +527,7 @@ uint64_t InMemoryReplicationHandlers::ReadAndApplyDelta(storage::InMemoryStorage
       case WalDeltaData::Type::EDGE_SET_PROPERTY: {
         spdlog::trace("       Edge {} set property {} to {}", delta.vertex_edge_set_property.gid.AsUint(),
                       delta.vertex_edge_set_property.property, delta.vertex_edge_set_property.value);
-        if (!storage->config_.items.properties_on_edges)
+        if (!storage->config_.salient.items.properties_on_edges)
           throw utils::BasicException(
               "Can't set properties on edges because properties on edges "
               "are disabled!");
@@ -572,8 +594,8 @@ uint64_t InMemoryReplicationHandlers::ReadAndApplyDelta(storage::InMemoryStorage
         spdlog::trace("       Transaction end");
         if (!commit_timestamp_and_accessor || commit_timestamp_and_accessor->first != timestamp)
           throw utils::BasicException("Invalid commit data!");
-        auto ret =
-            commit_timestamp_and_accessor->second.Commit(commit_timestamp_and_accessor->first, false /* not main */);
+        auto ret = commit_timestamp_and_accessor->second.Commit(
+            {.desired_commit_timestamp = commit_timestamp_and_accessor->first, .is_main = false});
         if (ret.HasError())
           throw utils::BasicException("Invalid transaction! Please raise an issue, {}:{}", __FILE__, __LINE__);
         commit_timestamp_and_accessor = std::nullopt;

src/dbms/inmemory/replication_handlers.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -12,7 +12,6 @@
 #pragma once
 
 #include "replication/replication_server.hpp"
-#include "replication/state.hpp"
 #include "storage/v2/replication/serialization.hpp"
 
 namespace memgraph::storage {

src/dbms/inmemory/storage_helper.hpp

@@ -24,8 +24,7 @@ namespace memgraph::dbms {
 
 inline std::unique_ptr<storage::Storage> CreateInMemoryStorage(storage::Config config,
                                                                ::memgraph::replication::ReplicationState &repl_state) {
-  const auto wal_mode = config.durability.snapshot_wal_mode;
-  const auto name = config.name;
+  const auto name = config.salient.name;
   auto storage = std::make_unique<storage::InMemoryStorage>(std::move(config));
 
   // Connect replication state and storage
@@ -34,24 +33,6 @@ inline std::unique_ptr<storage::Storage> CreateInMemoryStorage(storage::Config c
         return storage->CreateSnapshot(repl_state.GetRole());
       });
 
-  if (allow_mt_repl || name == dbms::kDefaultDB) {
-    // Handle global replication state
-    spdlog::info("Replication configuration will be stored and will be automatically restored in case of a crash.");
-    // RECOVER REPLICA CONNECTIONS
-    memgraph::dbms::RestoreReplication(repl_state, *storage);
-  } else if (const ::memgraph::replication::RoleMainData *data =
-                 std::get_if<::memgraph::replication::RoleMainData>(&repl_state.ReplicationData());
-             data && !data->registered_replicas_.empty()) {
-    spdlog::warn("Multi-tenant replication is currently not supported!");
-  }
-
-  if (wal_mode == storage::Config::Durability::SnapshotWalMode::DISABLED && repl_state.IsMain()) {
-    spdlog::warn(
-        "The instance has the MAIN replication role, but durability logs and snapshots are disabled. Please consider "
-        "enabling durability by using --storage-snapshot-interval-sec and --storage-wal-enabled flags because "
-        "without write-ahead logs this instance is not replicating any data.");
-  }
-
   return std::move(storage);
 }
 

src/dbms/replication_client.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -10,6 +10,7 @@
 // licenses/APL.txt.
 
 #include "dbms/replication_client.hpp"
+#include "replication/replication_client.hpp"
 
 namespace memgraph::dbms {
 
@@ -17,18 +18,26 @@ void StartReplicaClient(DbmsHandler &dbms_handler, replication::ReplicationClien
   // No client error, start instance level client
   auto const &endpoint = client.rpc_client_.Endpoint();
   spdlog::trace("Replication client started at: {}:{}", endpoint.address, endpoint.port);
-  client.StartFrequentCheck([&dbms_handler](std::string_view name) {
-    // Working connection, check if any database has been left behind
-    dbms_handler.ForEach([name](dbms::Database *db) {
+  client.StartFrequentCheck([&dbms_handler](bool reconnect, replication::ReplicationClient &client) {
+    // Working connection
+    // Check if system needs restoration
+    if (reconnect) {
+      client.state_.WithLock([](auto &state) { state = memgraph::replication::ReplicationClient::State::BEHIND; });
+    }
+#ifdef MG_ENTERPRISE
+    dbms_handler.SystemRestore<true>(client);
+#endif
+    // Check if any database has been left behind
+    dbms_handler.ForEach([&name = client.name_, reconnect](dbms::DatabaseAccess db_acc) {
       // Specific database <-> replica client
-      db->storage()->repl_storage_state_.WithClient(name, [&](storage::ReplicationStorageClient *client) {
-        if (client->State() == storage::replication::ReplicaState::MAYBE_BEHIND) {
+      db_acc->storage()->repl_storage_state_.WithClient(name, [&](storage::ReplicationStorageClient *client) {
+        if (reconnect || client->State() == storage::replication::ReplicaState::MAYBE_BEHIND) {
           // Database <-> replica might be behind, check and recover
-          client->TryCheckReplicaStateAsync(db->storage());
+          client->TryCheckReplicaStateAsync(db_acc->storage(), db_acc);
         }
       });
     });
   });
-}
+}  // namespace memgraph::dbms
 
 }  // namespace memgraph::dbms

src/dbms/replication_handler.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -11,15 +11,21 @@
 
 #include "dbms/replication_handler.hpp"
 
+#include <algorithm>
+
 #include "dbms/constants.hpp"
 #include "dbms/dbms_handler.hpp"
+#include "dbms/global.hpp"
 #include "dbms/inmemory/replication_handlers.hpp"
-#include "dbms/inmemory/storage_helper.hpp"
 #include "dbms/replication_client.hpp"
+#include "dbms/utils.hpp"
+#include "replication/messages.hpp"
 #include "replication/state.hpp"
+#include "spdlog/spdlog.h"
+#include "storage/v2/config.hpp"
+#include "storage/v2/replication/rpc.hpp"
+#include "utils/on_scope_exit.hpp"
 
-using memgraph::replication::ReplicationClientConfig;
-using memgraph::replication::ReplicationState;
 using memgraph::replication::RoleMainData;
 using memgraph::replication::RoleReplicaData;
 
@@ -32,8 +38,8 @@ std::string RegisterReplicaErrorToString(RegisterReplicaError error) {
     using enum RegisterReplicaError;
     case NAME_EXISTS:
       return "NAME_EXISTS";
-    case END_POINT_EXISTS:
-      return "END_POINT_EXISTS";
+    case ENDPOINT_EXISTS:
+      return "ENDPOINT_EXISTS";
     case CONNECTION_FAILED:
       return "CONNECTION_FAILED";
     case COULD_NOT_BE_PERSISTED:
@@ -45,34 +51,13 @@ std::string RegisterReplicaErrorToString(RegisterReplicaError error) {
 ReplicationHandler::ReplicationHandler(DbmsHandler &dbms_handler) : dbms_handler_(dbms_handler) {}
 
 bool ReplicationHandler::SetReplicationRoleMain() {
-  auto const main_handler = [](RoleMainData const &) {
+  auto const main_handler = [](RoleMainData &) {
     // If we are already MAIN, we don't want to change anything
     return false;
   };
+
   auto const replica_handler = [this](RoleReplicaData const &) {
-    // STEP 1) bring down all REPLICA servers
-    dbms_handler_.ForEach([](Database *db) {
-      auto *storage = db->storage();
-      // Remember old epoch + storage timestamp association
-      storage->PrepareForNewEpoch();
-    });
-
-    // STEP 2) Change to MAIN
-    // TODO: restore replication servers if false?
-    if (!dbms_handler_.ReplicationState().SetReplicationRoleMain()) {
-      // TODO: Handle recovery on failure???
-      return false;
-    }
-
-    // STEP 3) We are now MAIN, update storage local epoch
-    const auto &epoch =
-        std::get<RoleMainData>(std::as_const(dbms_handler_.ReplicationState()).ReplicationData()).epoch_;
-    dbms_handler_.ForEach([&](Database *db) {
-      auto *storage = db->storage();
-      storage->repl_storage_state_.epoch_ = epoch;
-    });
-
-    return true;
+    return memgraph::dbms::DoReplicaToMainPromotion(dbms_handler_);
   };
 
   // TODO: under lock
@@ -89,8 +74,8 @@ bool ReplicationHandler::SetReplicationRoleReplica(const memgraph::replication::
   // TODO StorageState needs to be synched. Could have a dangling reference if someone adds a database as we are
   //      deleting the replica.
   // Remove database specific clients
-  dbms_handler_.ForEach([&](Database *db) {
-    auto *storage = db->storage();
+  dbms_handler_.ForEach([&](DatabaseAccess db_acc) {
+    auto *storage = db_acc->storage();
     storage->repl_storage_state_.replication_clients_.WithLock([](auto &clients) { clients.clear(); });
   });
   // Remove instance level clients
@@ -105,15 +90,7 @@ bool ReplicationHandler::SetReplicationRoleReplica(const memgraph::replication::
                                      // ASSERT
                                      return false;
                                    },
-                                   [this](RoleReplicaData const &data) {
-                                     // Register handlers
-                                     InMemoryReplicationHandlers::Register(&dbms_handler_, *data.server);
-                                     if (!data.server->Start()) {
-                                       spdlog::error("Unable to start the replication server.");
-                                       return false;
-                                     }
-                                     return true;
-                                   }},
+                                   [this](RoleReplicaData const &data) { return StartRpcServer(dbms_handler_, data); }},
                  dbms_handler_.ReplicationState().ReplicationData());
   // TODO Handle error (restore to main?)
   return success;
@@ -123,60 +100,48 @@ auto ReplicationHandler::RegisterReplica(const memgraph::replication::Replicatio
     -> memgraph::utils::BasicResult<RegisterReplicaError> {
   MG_ASSERT(dbms_handler_.ReplicationState().IsMain(), "Only main instance can register a replica!");
 
-  auto instance_client = dbms_handler_.ReplicationState().RegisterReplica(config);
-  if (instance_client.HasError()) switch (instance_client.GetError()) {
+  auto maybe_client = dbms_handler_.ReplicationState().RegisterReplica(config);
+  if (maybe_client.HasError()) {
+    switch (maybe_client.GetError()) {
       case memgraph::replication::RegisterReplicaError::NOT_MAIN:
         MG_ASSERT(false, "Only main instance can register a replica!");
         return {};
       case memgraph::replication::RegisterReplicaError::NAME_EXISTS:
         return memgraph::dbms::RegisterReplicaError::NAME_EXISTS;
-      case memgraph::replication::RegisterReplicaError::END_POINT_EXISTS:
-        return memgraph::dbms::RegisterReplicaError::END_POINT_EXISTS;
+      case memgraph::replication::RegisterReplicaError::ENDPOINT_EXISTS:
+        return memgraph::dbms::RegisterReplicaError::ENDPOINT_EXISTS;
       case memgraph::replication::RegisterReplicaError::COULD_NOT_BE_PERSISTED:
         return memgraph::dbms::RegisterReplicaError::COULD_NOT_BE_PERSISTED;
       case memgraph::replication::RegisterReplicaError::SUCCESS:
         break;
     }
+  }
 
   if (!allow_mt_repl && dbms_handler_.All().size() > 1) {
     spdlog::warn("Multi-tenant replication is currently not supported!");
   }
 
-  bool all_clients_good = true;
+#ifdef MG_ENTERPRISE
+  // Update system before enabling individual storage <-> replica clients
+  dbms_handler_.SystemRestore(*maybe_client.GetValue());
+#endif
 
-  // Add database specific clients (NOTE Currently all databases are connected to each replica)
-  dbms_handler_.ForEach([&](Database *db) {
-    auto *storage = db->storage();
-    if (!allow_mt_repl && storage->id() != kDefaultDB) {
-      return;
-    }
-    // TODO: ATM only IN_MEMORY_TRANSACTIONAL, fix other modes
-    if (storage->storage_mode_ != storage::StorageMode::IN_MEMORY_TRANSACTIONAL) return;
-
-    all_clients_good &=
-        storage->repl_storage_state_.replication_clients_.WithLock([storage, &instance_client](auto &storage_clients) {
-          auto client = std::make_unique<storage::ReplicationStorageClient>(*instance_client.GetValue());
-          client->Start(storage);
-          // After start the storage <-> replica state should be READY or RECOVERING (if correctly started)
-          // MAYBE_BEHIND isn't a statement of the current state, this is the default value
-          // Failed to start due to branching of MAIN and REPLICA
-          if (client->State() == storage::replication::ReplicaState::MAYBE_BEHIND) {
-            return false;
-          }
-          storage_clients.push_back(std::move(client));
-          return true;
-        });
-  });
+  const auto dbms_error = memgraph::dbms::HandleRegisterReplicaStatus(maybe_client);
+  if (dbms_error.has_value()) {
+    return *dbms_error;
+  }
+  auto &instance_client_ptr = maybe_client.GetValue();
+  const bool all_clients_good = memgraph::dbms::RegisterAllDatabasesClients(dbms_handler_, *instance_client_ptr);
 
   // NOTE Currently if any databases fails, we revert back
   if (!all_clients_good) {
-    spdlog::error("Failed to register all databases to the REPLICA \"{}\"", config.name);
+    spdlog::error("Failed to register all databases on the REPLICA \"{}\"", config.name);
     UnregisterReplica(config.name);
     return RegisterReplicaError::CONNECTION_FAILED;
   }
 
   // No client error, start instance level client
-  StartReplicaClient(dbms_handler_, *instance_client.GetValue());
+  StartReplicaClient(dbms_handler_, *instance_client_ptr);
   return {};
 }
 
@@ -189,8 +154,8 @@ auto ReplicationHandler::UnregisterReplica(std::string_view name) -> UnregisterR
       return UnregisterReplicaResult::COULD_NOT_BE_PERSISTED;
     }
     // Remove database specific clients
-    dbms_handler_.ForEach([name](Database *db) {
-      db->storage()->repl_storage_state_.replication_clients_.WithLock([&name](auto &clients) {
+    dbms_handler_.ForEach([name](DatabaseAccess db_acc) {
+      db_acc->storage()->repl_storage_state_.replication_clients_.WithLock([&name](auto &clients) {
         std::erase_if(clients, [name](const auto &client) { return client->Name() == name; });
       });
     });
@@ -204,7 +169,7 @@ auto ReplicationHandler::UnregisterReplica(std::string_view name) -> UnregisterR
                     dbms_handler_.ReplicationState().ReplicationData());
 }
 
-auto ReplicationHandler::GetRole() const -> memgraph::replication::ReplicationRole {
+auto ReplicationHandler::GetRole() const -> memgraph::replication_coordination_glue::ReplicationRole {
   return dbms_handler_.ReplicationState().GetRole();
 }
 
@@ -214,20 +179,20 @@ bool ReplicationHandler::IsReplica() const { return dbms_handler_.ReplicationSta
 
 // Per storage
 // NOTE Storage will connect to all replicas. Future work might change this
-void RestoreReplication(replication::ReplicationState &repl_state, storage::Storage &storage) {
+void RestoreReplication(replication::ReplicationState &repl_state, DatabaseAccess db_acc) {
   spdlog::info("Restoring replication role.");
 
   /// MAIN
-  auto const recover_main = [&storage](RoleMainData &mainData) {
+  auto const recover_main = [db_acc = std::move(db_acc)](RoleMainData &mainData) mutable {  // NOLINT
     // Each individual client has already been restored and started. Here we just go through each database and start its
     // client
     for (auto &instance_client : mainData.registered_replicas_) {
-      spdlog::info("Replica {} restoration started for {}.", instance_client.name_, storage.id());
-
-      const auto &ret = storage.repl_storage_state_.replication_clients_.WithLock(
-          [&](auto &storage_clients) -> utils::BasicResult<RegisterReplicaError> {
+      spdlog::info("Replica {} restoration started for {}.", instance_client.name_, db_acc->name());
+      const auto &ret = db_acc->storage()->repl_storage_state_.replication_clients_.WithLock(
+          [&, db_acc](auto &storage_clients) mutable -> utils::BasicResult<RegisterReplicaError> {
             auto client = std::make_unique<storage::ReplicationStorageClient>(instance_client);
-            client->Start(&storage);
+            auto *storage = db_acc->storage();
+            client->Start(storage, std::move(db_acc));
             // After start the storage <-> replica state should be READY or RECOVERING (if correctly started)
             // MAYBE_BEHIND isn't a statement of the current state, this is the default value
             // Failed to start due to branching of MAIN and REPLICA
@@ -244,7 +209,7 @@ void RestoreReplication(replication::ReplicationState &repl_state, storage::Stor
         LOG_FATAL("Failure when restoring replica {}: {}.", instance_client.name_,
                   RegisterReplicaErrorToString(ret.GetError()));
       }
-      spdlog::info("Replica {} restored for {}.", instance_client.name_, storage.id());
+      spdlog::info("Replica {} restored for {}.", instance_client.name_, db_acc->name());
     }
     spdlog::info("Replication role restored to MAIN.");
   };
@@ -259,4 +224,177 @@ void RestoreReplication(replication::ReplicationState &repl_state, storage::Stor
       },
       repl_state.ReplicationData());
 }
+
+namespace system_replication {
+#ifdef MG_ENTERPRISE
+void SystemHeartbeatHandler(const uint64_t ts, slk::Reader *req_reader, slk::Builder *res_builder) {
+  replication::SystemHeartbeatReq req;
+  replication::SystemHeartbeatReq::Load(&req, req_reader);
+
+  replication::SystemHeartbeatRes res(ts);
+  memgraph::slk::Save(res, res_builder);
+}
+
+void CreateDatabaseHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader, slk::Builder *res_builder) {
+  memgraph::storage::replication::CreateDatabaseReq req;
+  memgraph::slk::Load(&req, req_reader);
+
+  using memgraph::storage::replication::CreateDatabaseRes;
+  CreateDatabaseRes res(CreateDatabaseRes::Result::FAILURE);
+
+  // Note: No need to check epoch, recovery mechanism is done by a full uptodate snapshot
+  //       of the set of databases. Hence no history exists to maintain regarding epoch change.
+  //       If MAIN has changed we need to check this new group_timestamp is consistent with
+  //       what we have so far.
+
+  if (req.expected_group_timestamp != dbms_handler.LastCommitedTS()) {
+    spdlog::debug("CreateDatabaseHandler: bad expected timestamp {},{}", req.expected_group_timestamp,
+                  dbms_handler.LastCommitedTS());
+    memgraph::slk::Save(res, res_builder);
+    return;
+  }
+
+  try {
+    // Create new
+    auto new_db = dbms_handler.Update(req.config);
+    if (new_db.HasValue()) {
+      // Successfully create db
+      dbms_handler.SetLastCommitedTS(req.new_group_timestamp);
+      res = CreateDatabaseRes(CreateDatabaseRes::Result::SUCCESS);
+      spdlog::debug("CreateDatabaseHandler: SUCCESS updated LCTS to {}", req.new_group_timestamp);
+    }
+  } catch (...) {
+    // Failure
+  }
+
+  memgraph::slk::Save(res, res_builder);
+}
+
+void DropDatabaseHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader, slk::Builder *res_builder) {
+  memgraph::storage::replication::DropDatabaseReq req;
+  memgraph::slk::Load(&req, req_reader);
+
+  using memgraph::storage::replication::DropDatabaseRes;
+  DropDatabaseRes res(DropDatabaseRes::Result::FAILURE);
+
+  // Note: No need to check epoch, recovery mechanism is done by a full uptodate snapshot
+  //       of the set of databases. Hence no history exists to maintain regarding epoch change.
+  //       If MAIN has changed we need to check this new group_timestamp is consistent with
+  //       what we have so far.
+
+  if (req.expected_group_timestamp != dbms_handler.LastCommitedTS()) {
+    spdlog::debug("DropDatabaseHandler: bad expected timestamp {},{}", req.expected_group_timestamp,
+                  dbms_handler.LastCommitedTS());
+    memgraph::slk::Save(res, res_builder);
+    return;
+  }
+
+  try {
+    // NOTE: Single communication channel can exist at a time, no other database can be deleted/created at the moment.
+    auto new_db = dbms_handler.Delete(req.uuid);
+    if (new_db.HasError()) {
+      if (new_db.GetError() == DeleteError::NON_EXISTENT) {
+        // Nothing to drop
+        dbms_handler.SetLastCommitedTS(req.new_group_timestamp);
+        res = DropDatabaseRes(DropDatabaseRes::Result::NO_NEED);
+      }
+    } else {
+      // Successfully drop db
+      dbms_handler.SetLastCommitedTS(req.new_group_timestamp);
+      res = DropDatabaseRes(DropDatabaseRes::Result::SUCCESS);
+      spdlog::debug("DropDatabaseHandler: SUCCESS updated LCTS to {}", req.new_group_timestamp);
+    }
+  } catch (...) {
+    // Failure
+  }
+
+  memgraph::slk::Save(res, res_builder);
+}
+
+void SystemRecoveryHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader, slk::Builder *res_builder) {
+  // TODO Speed up
+  memgraph::storage::replication::SystemRecoveryReq req;
+  memgraph::slk::Load(&req, req_reader);
+
+  using memgraph::storage::replication::SystemRecoveryRes;
+  SystemRecoveryRes res(SystemRecoveryRes::Result::FAILURE);
+
+  utils::OnScopeExit send_on_exit([&]() { memgraph::slk::Save(res, res_builder); });
+
+  // Get all current dbs
+  auto old = dbms_handler.All();
+
+  // Check/create the incoming dbs
+  for (const auto &config : req.database_configs) {
+    // Missing db
+    try {
+      if (dbms_handler.Update(config).HasError()) {
+        spdlog::debug("SystemRecoveryHandler: Failed to update database \"{}\".", config.name);
+        return;  // Send failure on exit
+      }
+    } catch (const UnknownDatabaseException &) {
+      spdlog::debug("SystemRecoveryHandler: UnknownDatabaseException");
+      return;  // Send failure on exit
+    }
+    const auto it = std::find(old.begin(), old.end(), config.name);
+    if (it != old.end()) old.erase(it);
+  }
+
+  // Delete all the leftover old dbs
+  for (const auto &remove_db : old) {
+    const auto del = dbms_handler.Delete(remove_db);
+    if (del.HasError()) {
+      // Some errors are not terminal
+      if (del.GetError() == DeleteError::DEFAULT_DB || del.GetError() == DeleteError::NON_EXISTENT) {
+        spdlog::debug("SystemRecoveryHandler: Dropped database \"{}\".", remove_db);
+        continue;
+      }
+      spdlog::debug("SystemRecoveryHandler: Failed to drop database \"{}\".", remove_db);
+      return;  // Send failure on exit
+    }
+  }
+  // Successfully recovered
+  dbms_handler.SetLastCommitedTS(req.forced_group_timestamp);
+  spdlog::debug("SystemRecoveryHandler: SUCCESS updated LCTS to {}", req.forced_group_timestamp);
+  res = SystemRecoveryRes(SystemRecoveryRes::Result::SUCCESS);
+}
+#endif
+
+void Register(replication::RoleReplicaData const &data, dbms::DbmsHandler &dbms_handler) {
+#ifdef MG_ENTERPRISE
+  data.server->rpc_server_.Register<replication::SystemHeartbeatRpc>(
+      [&dbms_handler](auto *req_reader, auto *res_builder) {
+        spdlog::debug("Received SystemHeartbeatRpc");
+        SystemHeartbeatHandler(dbms_handler.LastCommitedTS(), req_reader, res_builder);
+      });
+  data.server->rpc_server_.Register<storage::replication::CreateDatabaseRpc>(
+      [&dbms_handler](auto *req_reader, auto *res_builder) {
+        spdlog::debug("Received CreateDatabaseRpc");
+        CreateDatabaseHandler(dbms_handler, req_reader, res_builder);
+      });
+  data.server->rpc_server_.Register<storage::replication::DropDatabaseRpc>(
+      [&dbms_handler](auto *req_reader, auto *res_builder) {
+        spdlog::debug("Received DropDatabaseRpc");
+        DropDatabaseHandler(dbms_handler, req_reader, res_builder);
+      });
+  data.server->rpc_server_.Register<storage::replication::SystemRecoveryRpc>(
+      [&dbms_handler](auto *req_reader, auto *res_builder) {
+        spdlog::debug("Received SystemRecoveryRpc");
+        SystemRecoveryHandler(dbms_handler, req_reader, res_builder);
+      });
+#endif
+}
+}  // namespace system_replication
+
+bool StartRpcServer(DbmsHandler &dbms_handler, const replication::RoleReplicaData &data) {
+  // Register handlers
+  InMemoryReplicationHandlers::Register(&dbms_handler, *data.server);
+  system_replication::Register(data, dbms_handler);
+  // Start server
+  if (!data.server->Start()) {
+    spdlog::error("Unable to start the replication server.");
+    return false;
+  }
+  return true;
+}
 }  // namespace memgraph::dbms

src/dbms/replication_handler.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -11,11 +11,10 @@
 
 #pragma once
 
-#include "replication/role.hpp"
-#include "storage/v2/storage.hpp"
+#include "replication_coordination_glue/role.hpp"
+#include "dbms/database.hpp"
 #include "utils/result.hpp"
 
-// BEGIN fwd declares
 namespace memgraph::replication {
 struct ReplicationState;
 struct ReplicationServerConfig;
@@ -23,9 +22,11 @@ struct ReplicationClientConfig;
 }  // namespace memgraph::replication
 
 namespace memgraph::dbms {
+
 class DbmsHandler;
 
-enum class RegisterReplicaError : uint8_t { NAME_EXISTS, END_POINT_EXISTS, CONNECTION_FAILED, COULD_NOT_BE_PERSISTED };
+enum class RegisterReplicaError : uint8_t { NAME_EXISTS, ENDPOINT_EXISTS, CONNECTION_FAILED, COULD_NOT_BE_PERSISTED };
+
 enum class UnregisterReplicaResult : uint8_t {
   NOT_MAIN,
   COULD_NOT_BE_PERSISTED,
@@ -52,7 +53,7 @@ struct ReplicationHandler {
   auto UnregisterReplica(std::string_view name) -> UnregisterReplicaResult;
 
   // Helper pass-through (TODO: remove)
-  auto GetRole() const -> memgraph::replication::ReplicationRole;
+  auto GetRole() const -> memgraph::replication_coordination_glue::ReplicationRole;
   bool IsMain() const;
   bool IsReplica() const;
 
@@ -62,6 +63,20 @@ struct ReplicationHandler {
 
 /// A handler type that keep in sync current ReplicationState and the MAIN/REPLICA-ness of Storage
 /// TODO: extend to do multiple storages
-void RestoreReplication(replication::ReplicationState &repl_state, storage::Storage &storage);
+void RestoreReplication(replication::ReplicationState &repl_state, DatabaseAccess db_acc);
+
+namespace system_replication {
+// System handlers
+#ifdef MG_ENTERPRISE
+void CreateDatabaseHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader, slk::Builder *res_builder);
+void SystemHeartbeatHandler(uint64_t ts, slk::Reader *req_reader, slk::Builder *res_builder);
+void SystemRecoveryHandler(DbmsHandler &dbms_handler, slk::Reader *req_reader, slk::Builder *res_builder);
+#endif
+
+/// Register all DBMS level RPC handlers
+void Register(replication::RoleReplicaData const &data, DbmsHandler &dbms_handler);
+}  // namespace system_replication
+
+bool StartRpcServer(DbmsHandler &dbms_handler, const replication::RoleReplicaData &data);
 
 }  // namespace memgraph::dbms

src/dbms/transaction.hpp

@@ -0,0 +1,64 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#include <memory>
+#include "storage/v2/config.hpp"
+
+namespace memgraph::dbms {
+struct SystemTransaction {
+  struct Delta {
+    enum class Action {
+      CREATE_DATABASE,
+      DROP_DATABASE,
+    };
+
+    static constexpr struct CreateDatabase {
+    } create_database;
+    static constexpr struct DropDatabase {
+    } drop_database;
+
+    Delta(CreateDatabase /*tag*/, storage::SalientConfig config)
+        : action(Action::CREATE_DATABASE), config(std::move(config)) {}
+    Delta(DropDatabase /*tag*/, const utils::UUID &uuid) : action(Action::DROP_DATABASE), uuid(uuid) {}
+
+    Delta(const Delta &) = delete;
+    Delta(Delta &&) = delete;
+    Delta &operator=(const Delta &) = delete;
+    Delta &operator=(Delta &&) = delete;
+
+    ~Delta() {
+      switch (action) {
+        case Action::CREATE_DATABASE:
+          std::destroy_at(&config);
+          break;
+        case Action::DROP_DATABASE:
+          break;
+          // Some deltas might have special destructor handling
+      }
+    }
+
+    Action action;
+    union {
+      storage::SalientConfig config;
+      utils::UUID uuid;
+    };
+  };
+
+  explicit SystemTransaction(uint64_t timestamp) : system_timestamp(timestamp) {}
+
+  // Currently system transitions support a single delta
+  std::optional<Delta> delta{};
+  uint64_t system_timestamp;
+};
+
+}  // namespace memgraph::dbms

src/dbms/utils.hpp

@@ -0,0 +1,133 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+#pragma once
+
+#include "dbms/dbms_handler.hpp"
+#include "dbms/replication_handler.hpp"
+#include "replication/include/replication/state.hpp"
+#include "utils/result.hpp"
+
+namespace memgraph::dbms {
+
+inline bool DoReplicaToMainPromotion(dbms::DbmsHandler &dbms_handler) {
+  auto &repl_state = dbms_handler.ReplicationState();
+  // STEP 1) bring down all REPLICA servers
+  dbms_handler.ForEach([](DatabaseAccess db_acc) {
+    auto *storage = db_acc->storage();
+    // Remember old epoch + storage timestamp association
+    storage->PrepareForNewEpoch();
+  });
+
+  // STEP 2) Change to MAIN
+  // TODO: restore replication servers if false?
+  if (!repl_state.SetReplicationRoleMain()) {
+    // TODO: Handle recovery on failure???
+    return false;
+  }
+
+  // STEP 3) We are now MAIN, update storage local epoch
+  const auto &epoch =
+      std::get<replication::RoleMainData>(std::as_const(dbms_handler.ReplicationState()).ReplicationData()).epoch_;
+  dbms_handler.ForEach([&](DatabaseAccess db_acc) {
+    auto *storage = db_acc->storage();
+    storage->repl_storage_state_.epoch_ = epoch;
+  });
+
+  return true;
+};
+
+inline bool SetReplicationRoleReplica(dbms::DbmsHandler &dbms_handler,
+                                      const memgraph::replication::ReplicationServerConfig &config) {
+  if (dbms_handler.ReplicationState().IsReplica()) {
+    return false;
+  }
+
+  // TODO StorageState needs to be synched. Could have a dangling reference if someone adds a database as we are
+  //      deleting the replica.
+  // Remove database specific clients
+  dbms_handler.ForEach([&](DatabaseAccess db_acc) {
+    auto *storage = db_acc->storage();
+    storage->repl_storage_state_.replication_clients_.WithLock([](auto &clients) { clients.clear(); });
+  });
+  // Remove instance level clients
+  std::get<replication::RoleMainData>(dbms_handler.ReplicationState().ReplicationData()).registered_replicas_.clear();
+
+  // Creates the server
+  dbms_handler.ReplicationState().SetReplicationRoleReplica(config);
+
+  // Start
+  const auto success = std::visit(utils::Overloaded{[](replication::RoleMainData const &) {
+                                                      // ASSERT
+                                                      return false;
+                                                    },
+                                                    [&dbms_handler](replication::RoleReplicaData const &data) {
+                                                      return StartRpcServer(dbms_handler, data);
+                                                    }},
+                                  dbms_handler.ReplicationState().ReplicationData());
+  // TODO Handle error (restore to main?)
+  return success;
+}
+
+inline bool RegisterAllDatabasesClients(dbms::DbmsHandler &dbms_handler,
+                                        replication::ReplicationClient &instance_client) {
+  if (!allow_mt_repl && dbms_handler.All().size() > 1) {
+    spdlog::warn("Multi-tenant replication is currently not supported!");
+  }
+
+  bool all_clients_good = true;
+
+  // Add database specific clients (NOTE Currently all databases are connected to each replica)
+  dbms_handler.ForEach([&](DatabaseAccess db_acc) {
+    auto *storage = db_acc->storage();
+    if (!allow_mt_repl && storage->name() != kDefaultDB) {
+      return;
+    }
+    // TODO: ATM only IN_MEMORY_TRANSACTIONAL, fix other modes
+    if (storage->storage_mode_ != storage::StorageMode::IN_MEMORY_TRANSACTIONAL) return;
+
+    all_clients_good &= storage->repl_storage_state_.replication_clients_.WithLock(
+        [storage, &instance_client, db_acc = std::move(db_acc)](auto &storage_clients) mutable {  // NOLINT
+          auto client = std::make_unique<storage::ReplicationStorageClient>(instance_client);
+          // All good, start replica client
+          client->Start(storage, std::move(db_acc));
+          // After start the storage <-> replica state should be READY or RECOVERING (if correctly started)
+          // MAYBE_BEHIND isn't a statement of the current state, this is the default value
+          // Failed to start due an error like branching of MAIN and REPLICA
+          if (client->State() == storage::replication::ReplicaState::MAYBE_BEHIND) {
+            return false;  // TODO: sometimes we need to still add to storage_clients
+          }
+          storage_clients.push_back(std::move(client));
+          return true;
+        });
+  });
+
+  return all_clients_good;
+}
+
+inline std::optional<RegisterReplicaError> HandleRegisterReplicaStatus(
+    utils::BasicResult<replication::RegisterReplicaError, replication::ReplicationClient *> &instance_client) {
+  if (instance_client.HasError()) switch (instance_client.GetError()) {
+      case replication::RegisterReplicaError::NOT_MAIN:
+        MG_ASSERT(false, "Only main instance can register a replica!");
+        return {};
+      case replication::RegisterReplicaError::NAME_EXISTS:
+        return dbms::RegisterReplicaError::NAME_EXISTS;
+      case replication::RegisterReplicaError::ENDPOINT_EXISTS:
+        return dbms::RegisterReplicaError::ENDPOINT_EXISTS;
+      case replication::RegisterReplicaError::COULD_NOT_BE_PERSISTED:
+        return dbms::RegisterReplicaError::COULD_NOT_BE_PERSISTED;
+      case replication::RegisterReplicaError::SUCCESS:
+        break;
+    }
+  return {};
+}
+
+}  // namespace memgraph::dbms

src/flags/CMakeLists.txt

@@ -6,6 +6,7 @@ add_library(mg-flags STATIC audit.cpp
                             memory_limit.cpp
                             run_time_configurable.cpp
                             storage_mode.cpp
-                            query.cpp)
+                            query.cpp
+                            replication.cpp)
 target_include_directories(mg-flags PUBLIC ${CMAKE_SOURCE_DIR}/include)
 target_link_libraries(mg-flags PUBLIC spdlog::spdlog mg-settings mg-utils)

src/flags/all.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -17,5 +17,6 @@
 #include "flags/log_level.hpp"
 #include "flags/memory_limit.hpp"
 #include "flags/query.hpp"
+#include "flags/replication.hpp"
 #include "flags/run_time_configurable.hpp"
 #include "flags/storage_mode.hpp"

src/flags/general.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -131,12 +131,6 @@ DEFINE_uint64(storage_recovery_thread_count,
 DEFINE_bool(storage_enable_schema_metadata, false,
             "Controls whether metadata should be collected about the resident labels and edge types.");
 
-#ifdef MG_ENTERPRISE
-// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
-DEFINE_bool(storage_delete_on_drop, true,
-            "If set to true the query 'DROP DATABASE x' will delete the underlying storage as well.");
-#endif
-
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
 DEFINE_bool(telemetry_enabled, false,
             "Set to true to enable telemetry. We collect information about the "
@@ -162,13 +156,6 @@ DEFINE_string(pulsar_service_url, "", "Default URL used while connecting to Puls
 
 // Query flags.
 
-// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
-DEFINE_uint64(replication_replica_check_frequency_sec, 1,
-              "The time duration between two replica checks/pings. If < 1, replicas will NOT be checked at all. NOTE: "
-              "The MAIN instance allocates a new thread for each REPLICA.");
-// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
-DEFINE_bool(replication_restore_state_on_startup, false, "Restore replication state on startup, e.g. recover replica");
-
 DEFINE_VALIDATED_string(query_modules_directory, "",
                         "Directory where modules with custom query procedures are stored. "
                         "NOTE: Multiple comma-separated directories can be defined.",

src/flags/general.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -84,10 +84,6 @@ DECLARE_bool(storage_parallel_schema_recovery);
 DECLARE_uint64(storage_recovery_thread_count);
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
 DECLARE_bool(storage_enable_schema_metadata);
-#ifdef MG_ENTERPRISE
-// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
-DECLARE_bool(storage_delete_on_drop);
-#endif
 
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
 DECLARE_bool(telemetry_enabled);
@@ -116,11 +112,6 @@ namespace memgraph::flags {
 auto ParseQueryModulesDirectory() -> std::vector<std::filesystem::path>;
 }  // namespace memgraph::flags
 
-// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
-DECLARE_uint64(replication_replica_check_frequency_sec);
-// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
-DECLARE_bool(replication_restore_state_on_startup);
-
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
 DECLARE_string(license_key);
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)

src/flags/replication.cpp

@@ -0,0 +1,26 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#include "replication.hpp"
+
+#ifdef MG_ENTERPRISE
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DEFINE_bool(coordinator, false, "Controls whether the instance is a replication coordinator.");
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DEFINE_uint32(coordinator_server_port, 0, "Port on which coordinator servers will be started.");
+#endif
+
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DEFINE_uint64(replication_replica_check_frequency_sec, 1,
+              "The time duration between two replica checks/pings. If < 1, replicas will NOT be checked at all. NOTE: "
+              "The MAIN instance allocates a new thread for each REPLICA.");
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DEFINE_bool(replication_restore_state_on_startup, false, "Restore replication state on startup, e.g. recover replica");

src/flags/replication.hpp

@@ -0,0 +1,26 @@
+// Copyright 2024 Memgraph Ltd.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+// License, and you may not use this file except in compliance with the Business Source License.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+#pragma once
+
+#include "gflags/gflags.h"
+
+#ifdef MG_ENTERPRISE
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DECLARE_bool(coordinator);
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DECLARE_uint32(coordinator_server_port);
+#endif
+
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DECLARE_uint64(replication_replica_check_frequency_sec);
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+DECLARE_bool(replication_restore_state_on_startup);

src/flags/storage_mode.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -17,20 +17,14 @@
 
 #include "gflags/gflags.h"
 
-#include <array>
-
-inline constexpr std::array storage_mode_mappings{
-    std::pair{std::string_view{"IN_MEMORY_TRANSACTIONAL"}, memgraph::storage::StorageMode::IN_MEMORY_TRANSACTIONAL},
-    std::pair{std::string_view{"IN_MEMORY_ANALYTICAL"}, memgraph::storage::StorageMode::IN_MEMORY_ANALYTICAL},
-    std::pair{std::string_view{"ON_DISK_TRANSACTIONAL"}, memgraph::storage::StorageMode::ON_DISK_TRANSACTIONAL}};
-
 const std::string storage_mode_help_string =
     fmt::format("Default storage mode Memgraph uses. Allowed values: {}",
-                memgraph::utils::GetAllowedEnumValuesString(storage_mode_mappings));
+                memgraph::utils::GetAllowedEnumValuesString(memgraph::storage::storage_mode_mappings));
 
 // NOLINTNEXTLINE (cppcoreguidelines-avoid-non-const-global-variables)
 DEFINE_VALIDATED_string(storage_mode, "IN_MEMORY_TRANSACTIONAL", storage_mode_help_string.c_str(), {
-  if (const auto result = memgraph::utils::IsValidEnumValueString(value, storage_mode_mappings); result.HasError()) {
+  if (const auto result = memgraph::utils::IsValidEnumValueString(value, memgraph::storage::storage_mode_mappings);
+      result.HasError()) {
     switch (result.GetError()) {
       case memgraph::utils::ValidationError::EmptyValue: {
         std::cout << "Storage mode cannot be empty." << std::endl;
@@ -38,7 +32,7 @@ DEFINE_VALIDATED_string(storage_mode, "IN_MEMORY_TRANSACTIONAL", storage_mode_he
       }
       case memgraph::utils::ValidationError::InvalidValue: {
         std::cout << "Invalid value for storage mode. Allowed values: "
-                  << memgraph::utils::GetAllowedEnumValuesString(storage_mode_mappings) << std::endl;
+                  << memgraph::utils::GetAllowedEnumValuesString(memgraph::storage::storage_mode_mappings) << std::endl;
         break;
       }
     }
@@ -48,8 +42,8 @@ DEFINE_VALIDATED_string(storage_mode, "IN_MEMORY_TRANSACTIONAL", storage_mode_he
 });
 
 memgraph::storage::StorageMode memgraph::flags::ParseStorageMode() {
-  const auto storage_mode =
-      memgraph::utils::StringToEnum<memgraph::storage::StorageMode>(FLAGS_storage_mode, storage_mode_mappings);
+  const auto storage_mode = memgraph::utils::StringToEnum<memgraph::storage::StorageMode>(
+      FLAGS_storage_mode, memgraph::storage::storage_mode_mappings);
   MG_ASSERT(storage_mode, "Invalid storage mode");
   return *storage_mode;
 }

src/glue/SessionHL.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -80,7 +80,7 @@ std::vector<memgraph::communication::bolt::Value> TypedValueResultStreamBase::De
   std::vector<memgraph::communication::bolt::Value> decoded_values;
   decoded_values.reserve(values.size());
   for (const auto &v : values) {
-    auto maybe_value = memgraph::glue::ToBoltValue(v, *storage_, memgraph::storage::View::NEW);
+    auto maybe_value = memgraph::glue::ToBoltValue(v, storage_, memgraph::storage::View::NEW);
     if (maybe_value.HasError()) {
       switch (maybe_value.GetError()) {
         case memgraph::storage::Error::DELETED_OBJECT:
@@ -112,14 +112,14 @@ std::string SessionHL::GetDefaultDB() {
   if (user_.has_value()) {
     return user_->db_access().GetDefault();
   }
-  return memgraph::dbms::kDefaultDB;
+  return std::string{memgraph::dbms::kDefaultDB};
 }
 #endif
 
 std::string SessionHL::GetCurrentDB() const {
   if (!interpreter_.current_db_.db_acc_) return "";
   const auto *db = interpreter_.current_db_.db_acc_->get();
-  return db->id();
+  return db->name();
 }
 
 std::optional<std::string> SessionHL::GetServerNameForInit() {
@@ -167,10 +167,10 @@ std::map<std::string, memgraph::communication::bolt::Value> SessionHL::Discard(s
 std::map<std::string, memgraph::communication::bolt::Value> SessionHL::Pull(SessionHL::TEncoder *encoder,
                                                                             std::optional<int> n,
                                                                             std::optional<int> qid) {
-  // TODO: Update once interpreter can handle non-database queries (db_acc will be nullopt)
-  auto *db = interpreter_.current_db_.db_acc_->get();
   try {
-    TypedValueResultStream<TEncoder> stream(encoder, db->storage());
+    auto &db = interpreter_.current_db_.db_acc_;
+    auto *storage = db ? db->get()->storage() : nullptr;
+    TypedValueResultStream<TEncoder> stream(encoder, storage);
     return DecodeSummary(interpreter_.Pull(&stream, n, qid));
   } catch (const memgraph::query::QueryException &e) {
     // Count the number of specific exceptions thrown
@@ -193,17 +193,17 @@ std::pair<std::vector<std::string>, std::optional<int>> SessionHL::Interpret(
   for (const auto &[key, bolt_param] : params) {
     params_pv.emplace(key, ToPropertyValue(bolt_param));
   }
+
+#ifdef MG_ENTERPRISE
   const std::string *username{nullptr};
   if (user_) {
     username = &user_->username();
   }
 
-#ifdef MG_ENTERPRISE
-  // TODO: Update once interpreter can handle non-database queries (db_acc will be nullopt)
-  auto *db = interpreter_.current_db_.db_acc_->get();
   if (memgraph::license::global_license_checker.IsEnterpriseValidFast()) {
+    auto &db = interpreter_.current_db_.db_acc_;
     audit_log_->Record(endpoint_.address().to_string(), user_ ? *username : "", query,
-                       memgraph::storage::PropertyValue(params_pv), db->id());
+                       memgraph::storage::PropertyValue(params_pv), db ? db->get()->name() : "no known database");
   }
 #endif
   try {
@@ -351,11 +351,11 @@ SessionHL::~SessionHL() {
 
 std::map<std::string, memgraph::communication::bolt::Value> SessionHL::DecodeSummary(
     const std::map<std::string, memgraph::query::TypedValue> &summary) {
-  // TODO: Update once interpreter can handle non-database queries (db_acc will be nullopt)
-  auto *db = interpreter_.current_db_.db_acc_->get();
+  auto &db_acc = interpreter_.current_db_.db_acc_;
+  auto *storage = db_acc ? db_acc->get()->storage() : nullptr;
   std::map<std::string, memgraph::communication::bolt::Value> decoded_summary;
   for (const auto &kv : summary) {
-    auto maybe_value = ToBoltValue(kv.second, *db->storage(), memgraph::storage::View::NEW);
+    auto maybe_value = ToBoltValue(kv.second, storage, memgraph::storage::View::NEW);
     if (maybe_value.HasError()) {
       switch (maybe_value.GetError()) {
         case memgraph::storage::Error::DELETED_OBJECT:

src/glue/auth.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -66,6 +66,8 @@ auth::Permission PrivilegeToPermission(query::AuthQuery::Privilege privilege) {
       return auth::Permission::MULTI_DATABASE_EDIT;
     case query::AuthQuery::Privilege::MULTI_DATABASE_USE:
       return auth::Permission::MULTI_DATABASE_USE;
+    case query::AuthQuery::Privilege::COORDINATOR:
+      return auth::Permission::COORDINATOR;
   }
 }
 

src/glue/auth_handler.cpp

@@ -294,7 +294,7 @@ bool AuthQueryHandler::CreateUser(const std::string &username, const std::option
       );
 #ifdef MG_ENTERPRISE
       GrantDatabaseToUser(auth::kAllDatabases, username);
-      SetMainDatabase(username, dbms::kDefaultDB);
+      SetMainDatabase(dbms::kDefaultDB, username);
 #endif
     }
 
@@ -393,7 +393,7 @@ std::vector<std::vector<memgraph::query::TypedValue>> AuthQueryHandler::GetDatab
   }
 }
 
-bool AuthQueryHandler::SetMainDatabase(const std::string &db, const std::string &username) {
+bool AuthQueryHandler::SetMainDatabase(std::string_view db, const std::string &username) {
   if (!std::regex_match(username, name_regex_)) {
     throw memgraph::query::QueryRuntimeException("Invalid user name.");
   }

src/glue/auth_handler.hpp

@@ -44,7 +44,7 @@ class AuthQueryHandler final : public memgraph::query::AuthQueryHandler {
 
   std::vector<std::vector<memgraph::query::TypedValue>> GetDatabasePrivileges(const std::string &username) override;
 
-  bool SetMainDatabase(const std::string &db, const std::string &username) override;
+  bool SetMainDatabase(std::string_view db, const std::string &username) override;
 
   void DeleteDatabase(std::string_view db) override;
 #endif

src/glue/communication.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -73,8 +73,14 @@ storage::Result<communication::bolt::Edge> ToBoltEdge(const query::EdgeAccessor
   return ToBoltEdge(edge.impl_, db, view);
 }
 
-storage::Result<Value> ToBoltValue(const query::TypedValue &value, const storage::Storage &db, storage::View view) {
+storage::Result<Value> ToBoltValue(const query::TypedValue &value, const storage::Storage *db, storage::View view) {
+  auto check_db = [db]() {
+    if (db == nullptr) [[unlikely]]
+      throw communication::bolt::ValueException("Database needed for TypeValue conversion.");
+  };
+
   switch (value.type()) {
+    // No database needed
     case query::TypedValue::Type::Null:
       return Value();
     case query::TypedValue::Type::Bool:
@@ -85,16 +91,16 @@ storage::Result<Value> ToBoltValue(const query::TypedValue &value, const storage
       return Value(value.ValueDouble());
     case query::TypedValue::Type::String:
       return Value(std::string(value.ValueString()));
-    case query::TypedValue::Type::List: {
-      std::vector<Value> values;
-      values.reserve(value.ValueList().size());
-      for (const auto &v : value.ValueList()) {
-        auto maybe_value = ToBoltValue(v, db, view);
-        if (maybe_value.HasError()) return maybe_value.GetError();
-        values.emplace_back(std::move(*maybe_value));
-      }
-      return Value(std::move(values));
-    }
+    case query::TypedValue::Type::Date:
+      return Value(value.ValueDate());
+    case query::TypedValue::Type::LocalTime:
+      return Value(value.ValueLocalTime());
+    case query::TypedValue::Type::LocalDateTime:
+      return Value(value.ValueLocalDateTime());
+    case query::TypedValue::Type::Duration:
+      return Value(value.ValueDuration());
+
+    // Database potentially not required
     case query::TypedValue::Type::Map: {
       std::map<std::string, Value> map;
       for (const auto &kv : value.ValueMap()) {
@@ -104,35 +110,48 @@ storage::Result<Value> ToBoltValue(const query::TypedValue &value, const storage
       }
       return Value(std::move(map));
     }
+
+    // Database is required
+    case query::TypedValue::Type::List: {
+      check_db();
+      std::vector<Value> values;
+      values.reserve(value.ValueList().size());
+      for (const auto &v : value.ValueList()) {
+        auto maybe_value = ToBoltValue(v, db, view);
+        if (maybe_value.HasError()) return maybe_value.GetError();
+        values.emplace_back(std::move(*maybe_value));
+      }
+      return Value(std::move(values));
+    }
     case query::TypedValue::Type::Vertex: {
-      auto maybe_vertex = ToBoltVertex(value.ValueVertex(), db, view);
+      check_db();
+      auto maybe_vertex = ToBoltVertex(value.ValueVertex(), *db, view);
       if (maybe_vertex.HasError()) return maybe_vertex.GetError();
       return Value(std::move(*maybe_vertex));
     }
     case query::TypedValue::Type::Edge: {
-      auto maybe_edge = ToBoltEdge(value.ValueEdge(), db, view);
+      check_db();
+      auto maybe_edge = ToBoltEdge(value.ValueEdge(), *db, view);
       if (maybe_edge.HasError()) return maybe_edge.GetError();
       return Value(std::move(*maybe_edge));
     }
     case query::TypedValue::Type::Path: {
-      auto maybe_path = ToBoltPath(value.ValuePath(), db, view);
+      check_db();
+      auto maybe_path = ToBoltPath(value.ValuePath(), *db, view);
       if (maybe_path.HasError()) return maybe_path.GetError();
       return Value(std::move(*maybe_path));
     }
-    case query::TypedValue::Type::Date:
-      return Value(value.ValueDate());
-    case query::TypedValue::Type::LocalTime:
-      return Value(value.ValueLocalTime());
-    case query::TypedValue::Type::LocalDateTime:
-      return Value(value.ValueLocalDateTime());
-    case query::TypedValue::Type::Duration:
-      return Value(value.ValueDuration());
-    case query::TypedValue::Type::Function:
-      throw communication::bolt::ValueException("Unsupported conversion from TypedValue::Function to Value");
-    case query::TypedValue::Type::Graph:
-      auto maybe_graph = ToBoltGraph(value.ValueGraph(), db, view);
+    case query::TypedValue::Type::Graph: {
+      check_db();
+      auto maybe_graph = ToBoltGraph(value.ValueGraph(), *db, view);
       if (maybe_graph.HasError()) return maybe_graph.GetError();
       return Value(std::move(*maybe_graph));
+    }
+
+    // Unsupported conversions
+    case query::TypedValue::Type::Function: {
+      throw communication::bolt::ValueException("Unsupported conversion from TypedValue::Function to Value");
+    }
   }
 }
 

src/glue/communication.hpp

@@ -1,4 +1,4 @@
-// Copyright 2022 Memgraph Ltd.
+// Copyright 2023 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -65,7 +65,7 @@ storage::Result<std::map<std::string, communication::bolt::Value>> ToBoltGraph(c
 /// @param storage::View for ToBoltVertex and ToBoltEdge.
 ///
 /// @throw std::bad_alloc
-storage::Result<communication::bolt::Value> ToBoltValue(const query::TypedValue &value, const storage::Storage &db,
+storage::Result<communication::bolt::Value> ToBoltValue(const query::TypedValue &value, const storage::Storage *db,
                                                         storage::View view);
 
 query::TypedValue ToTypedValue(const communication::bolt::Value &value);

src/io/CMakeLists.txt

@@ -8,4 +8,5 @@ find_package(fmt REQUIRED)
 find_package(Threads REQUIRED)
 
 add_library(mg-io STATIC ${io_src_files})
+add_library(mg::io ALIAS mg-io)
 target_link_libraries(mg-io stdc++fs Threads::Threads fmt::fmt mg-utils)

src/io/network/endpoint.cpp

@@ -166,7 +166,7 @@ bool Endpoint::IsResolvableAddress(const std::string &address, uint16_t port) {
 }
 
 std::optional<std::pair<std::string, uint16_t>> Endpoint::ParseSocketOrAddress(
-    const std::string &address, const std::optional<uint16_t> default_port = {}) {
+    const std::string &address, const std::optional<uint16_t> default_port) {
   const std::string delimiter = ":";
   std::vector<std::string> parts = utils::Split(address, delimiter);
   if (parts.size() == 1) {

src/kvstore/kvstore.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -51,7 +51,7 @@ KVStore &KVStore::operator=(KVStore &&other) {
   return *this;
 }
 
-bool KVStore::Put(const std::string &key, const std::string &value) {
+bool KVStore::Put(std::string_view key, std::string_view value) {
   auto s = pimpl_->db->Put(rocksdb::WriteOptions(), key, value);
   return s.ok();
 }
@@ -65,7 +65,7 @@ bool KVStore::PutMultiple(const std::map<std::string, std::string> &items) {
   return s.ok();
 }
 
-std::optional<std::string> KVStore::Get(const std::string &key) const noexcept {
+std::optional<std::string> KVStore::Get(std::string_view key) const noexcept {
   std::string value;
   auto s = pimpl_->db->Get(rocksdb::ReadOptions(), key, &value);
   if (!s.ok()) return std::nullopt;

src/kvstore/kvstore.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -61,7 +61,7 @@ class KVStore final {
    * @return true if the value has been successfully stored.
    *         In case of any error false is going to be returned.
    */
-  bool Put(const std::string &key, const std::string &value);
+  bool Put(std::string_view key, std::string_view value);
 
   /**
    * Store values under the given keys.
@@ -81,7 +81,7 @@ class KVStore final {
    * @return Value for the given key. std::nullopt in case of any error
    *         OR the value doesn't exist.
    */
-  std::optional<std::string> Get(const std::string &key) const noexcept;
+  std::optional<std::string> Get(std::string_view key) const noexcept;
 
   /**
    * Deletes the key and corresponding value from storage.

src/license/license.cpp

@@ -1,4 +1,4 @@
-// Copyright 2022 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -92,7 +92,7 @@ void RegisterLicenseSettings(LicenseChecker &license_checker, utils::Settings &s
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
 LicenseChecker global_license_checker;
 
-LicenseChecker::~LicenseChecker() { scheduler_.Stop(); }
+LicenseChecker::~LicenseChecker() { Finalize(); }
 
 std::pair<std::string, std::string> LicenseChecker::ExtractLicenseInfo(const utils::Settings &settings) const {
   if (license_info_override_) {

src/license/license.hpp

@@ -1,4 +1,4 @@
-// Copyright 2022 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -89,6 +89,8 @@ struct LicenseChecker {
 
   utils::Synchronized<std::optional<LicenseInfo>, utils::SpinLock> &GetLicenseInfo();
 
+  void Finalize() { scheduler_.Stop(); }
+
  private:
   std::pair<std::string, std::string> ExtractLicenseInfo(const utils::Settings &settings) const;
   void RevalidateLicense(const utils::Settings &settings);

src/memgraph.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -11,13 +11,11 @@
 
 #include <cstdint>
 #include "audit/log.hpp"
-#include "communication/metrics.hpp"
 #include "communication/websocket/auth.hpp"
 #include "communication/websocket/server.hpp"
 #include "dbms/constants.hpp"
 #include "dbms/inmemory/replication_handlers.hpp"
 #include "flags/all.hpp"
-#include "flags/run_time_configurable.hpp"
 #include "glue/MonitoringServerT.hpp"
 #include "glue/ServerT.hpp"
 #include "glue/auth_checker.hpp"
@@ -33,9 +31,9 @@
 #include "query/procedure/module.hpp"
 #include "query/procedure/py_module.hpp"
 #include "requests/requests.hpp"
+#include "storage/v2/durability/durability.hpp"
 #include "telemetry/telemetry.hpp"
 #include "utils/signals.hpp"
-#include "utils/skip_list.hpp"
 #include "utils/sysinfo/memory.hpp"
 #include "utils/system_info.hpp"
 #include "utils/terminate_handler.hpp"
@@ -73,7 +71,7 @@ void InitFromCypherlFile(memgraph::query::InterpreterContext &ctx, memgraph::dbm
         spdlog::warn("{} The rest of the init-file will be run.", e.what());
       }
       if (audit_log) {
-        audit_log->Record("", "", line, {}, memgraph::dbms::kDefaultDB);
+        audit_log->Record("", "", line, {}, std::string{memgraph::dbms::kDefaultDB});
       }
     }
   }
@@ -257,6 +255,8 @@ int main(int argc, char **argv) {
   // register all runtime settings
   memgraph::license::RegisterLicenseSettings(memgraph::license::global_license_checker,
                                              memgraph::utils::global_settings);
+  memgraph::utils::OnScopeExit global_license_finalizer([] { memgraph::license::global_license_checker.Finalize(); });
+
   memgraph::flags::run_time::Initialize();
 
   memgraph::license::global_license_checker.CheckEnvLicense();
@@ -298,8 +298,7 @@ int main(int argc, char **argv) {
   memgraph::storage::Config db_config{
       .gc = {.type = memgraph::storage::Config::Gc::Type::PERIODIC,
              .interval = std::chrono::seconds(FLAGS_storage_gc_cycle_sec)},
-      .items = {.properties_on_edges = FLAGS_storage_properties_on_edges,
-                .enable_schema_metadata = FLAGS_storage_enable_schema_metadata},
+
       .durability = {.storage_directory = FLAGS_data_directory,
                      .recover_on_startup = FLAGS_storage_recover_on_startup || FLAGS_data_recovery_on_startup,
                      .snapshot_retention_count = FLAGS_storage_snapshot_retention_count,
@@ -321,7 +320,9 @@ int main(int argc, char **argv) {
                .id_name_mapper_directory = FLAGS_data_directory + "/rocksdb_id_name_mapper",
                .durability_directory = FLAGS_data_directory + "/rocksdb_durability",
                .wal_directory = FLAGS_data_directory + "/rocksdb_wal"},
-      .storage_mode = memgraph::flags::ParseStorageMode()};
+      .salient.items = {.properties_on_edges = FLAGS_storage_properties_on_edges,
+                        .enable_schema_metadata = FLAGS_storage_enable_schema_metadata},
+      .salient.storage_mode = memgraph::flags::ParseStorageMode()};
 
   memgraph::utils::Scheduler jemalloc_purge_scheduler;
   jemalloc_purge_scheduler.Run("Jemalloc purge", std::chrono::seconds(FLAGS_storage_gc_cycle_sec),
@@ -386,7 +387,7 @@ int main(int argc, char **argv) {
   memgraph::dbms::DbmsHandler dbms_handler(db_config
 #ifdef MG_ENTERPRISE
                                            ,
-                                           &auth_, FLAGS_data_recovery_on_startup, FLAGS_storage_delete_on_drop
+                                           &auth_, FLAGS_data_recovery_on_startup
 #endif
   );
   auto db_acc = dbms_handler.Get();
@@ -546,6 +547,7 @@ int main(int argc, char **argv) {
 
   memgraph::query::procedure::gModuleRegistry.UnloadAllModules();
 
+  python_gc_scheduler.Stop();
   Py_END_ALLOW_THREADS;
   // Shutdown Python
   Py_Finalize();

src/mg_import_csv.cpp

@@ -32,7 +32,7 @@
 #include "utils/timer.hpp"
 #include "version.hpp"
 
-using memgraph::replication::ReplicationRole;
+using memgraph::replication_coordination_glue::ReplicationRole;
 
 bool ValidateControlCharacter(const char *flagname, const std::string &value) {
   if (value.empty()) {
@@ -707,12 +707,11 @@ int main(int argc, char *argv[]) {
 
   std::unordered_map<NodeId, memgraph::storage::Gid> node_id_map;
   memgraph::storage::Config config{
-
-      .items = {.properties_on_edges = FLAGS_storage_properties_on_edges},
       .durability = {.storage_directory = FLAGS_data_directory,
                      .recover_on_startup = false,
                      .snapshot_wal_mode = memgraph::storage::Config::Durability::SnapshotWalMode::DISABLED,
                      .snapshot_on_exit = true},
+      .salient = {.items = {.properties_on_edges = FLAGS_storage_properties_on_edges}},
   };
   memgraph::replication::ReplicationState repl_state{memgraph::storage::ReplicationStateRootPath(config)};
   auto store = memgraph::dbms::CreateInMemoryStorage(config, repl_state);

src/query/auth_query_handler.hpp

@@ -57,7 +57,7 @@ class AuthQueryHandler {
 
   /// Return true if main database set successfully
   /// @throw QueryRuntimeException if an error ocurred.
-  virtual bool SetMainDatabase(const std::string &db, const std::string &username) = 0;
+  virtual bool SetMainDatabase(std::string_view db, const std::string &username) = 0;
 
   /// Delete database from all users
   /// @throw QueryRuntimeException if an error ocurred.

src/query/common.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -72,8 +72,9 @@ class TypedValueVectorCompare final {
 
 /// Raise QueryRuntimeException if the value for symbol isn't of expected type.
 inline void ExpectType(const Symbol &symbol, const TypedValue &value, TypedValue::Type expected) {
-  if (value.type() != expected)
+  if (value.type() != expected) [[unlikely]] {
     throw QueryRuntimeException("Expected a {} for '{}', but got {}.", expected, symbol.name(), value.type());
+  }
 }
 
 inline void ProcessError(const storage::Error error) {

src/query/config.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source

src/query/context.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source

src/query/db_accessor.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -541,7 +541,10 @@ class DbAccessor final {
 
   void AdvanceCommand() { accessor_->AdvanceCommand(); }
 
-  utils::BasicResult<storage::StorageManipulationError, void> Commit() { return accessor_->Commit(); }
+  utils::BasicResult<storage::StorageManipulationError, void> Commit(storage::CommitReplArgs reparg = {},
+                                                                     storage::DatabaseAccessProtector db_acc = {}) {
+    return accessor_->Commit(std::move(reparg), std::move(db_acc));
+  }
 
   void Abort() { accessor_->Abort(); }
 

src/query/exceptions.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -195,6 +195,12 @@ class DatabaseContextRequiredException : public QueryRuntimeException {
   SPECIALIZE_GET_EXCEPTION_NAME(DatabaseContextRequiredException)
 };
 
+class ConcurrentSystemQueriesException : public QueryRuntimeException {
+ public:
+  using QueryRuntimeException::QueryRuntimeException;
+  SPECIALIZE_GET_EXCEPTION_NAME(ConcurrentSystemQueriesException)
+};
+
 class WriteVertexOperationInEdgeImportModeException : public QueryException {
  public:
   WriteVertexOperationInEdgeImportModeException()
@@ -253,6 +259,13 @@ class ReplicationModificationInMulticommandTxException : public QueryException {
   SPECIALIZE_GET_EXCEPTION_NAME(ReplicationModificationInMulticommandTxException)
 };
 
+class CoordinatorModificationInMulticommandTxException : public QueryException {
+ public:
+  CoordinatorModificationInMulticommandTxException()
+      : QueryException("Coordinator clause not allowed in multicommand transactions.") {}
+  SPECIALIZE_GET_EXCEPTION_NAME(CoordinatorModificationInMulticommandTxException)
+};
+
 class ReplicationDisabledOnDiskStorage : public QueryException {
  public:
   ReplicationDisabledOnDiskStorage() : QueryException("Replication is not supported while in on-disk storage mode.") {}

src/query/frontend/ast/ast.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -239,6 +239,9 @@ constexpr utils::TypeInfo query::DumpQuery::kType{utils::TypeId::AST_DUMP_QUERY,
 constexpr utils::TypeInfo query::ReplicationQuery::kType{utils::TypeId::AST_REPLICATION_QUERY, "ReplicationQuery",
                                                          &query::Query::kType};
 
+constexpr utils::TypeInfo query::CoordinatorQuery::kType{utils::TypeId::AST_COORDINATOR_QUERY, "CoordinatorQuery",
+                                                         &query::Query::kType};
+
 constexpr utils::TypeInfo query::LockPathQuery::kType{utils::TypeId::AST_LOCK_PATH_QUERY, "LockPathQuery",
                                                       &query::Query::kType};
 

src/query/frontend/ast/ast.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -1209,7 +1209,8 @@ class PropertyLookup : public memgraph::query::Expression {
   }
 
  protected:
-  PropertyLookup(Expression *expression, PropertyIx property) : expression_(expression), property_(property) {}
+  PropertyLookup(Expression *expression, PropertyIx property)
+      : expression_(expression), property_(std::move(property)) {}
 
  private:
   friend class AstStorage;
@@ -1805,9 +1806,9 @@ class EdgeAtom : public memgraph::query::PatternAtom {
   static const utils::TypeInfo kType;
   const utils::TypeInfo &GetTypeInfo() const override { return kType; }
 
-  enum class Type { SINGLE, DEPTH_FIRST, BREADTH_FIRST, WEIGHTED_SHORTEST_PATH, ALL_SHORTEST_PATHS };
+  enum class Type : uint8_t { SINGLE, DEPTH_FIRST, BREADTH_FIRST, WEIGHTED_SHORTEST_PATH, ALL_SHORTEST_PATHS };
 
-  enum class Direction { IN, OUT, BOTH };
+  enum class Direction : uint8_t { IN, OUT, BOTH };
 
   /// Lambda for use in filtering or weight calculation during variable expand.
   struct Lambda {
@@ -2216,7 +2217,7 @@ class IndexQuery : public memgraph::query::Query {
 
  protected:
   IndexQuery(Action action, LabelIx label, std::vector<PropertyIx> properties)
-      : action_(action), label_(label), properties_(properties) {}
+      : action_(action), label_(std::move(label)), properties_(std::move(properties)) {}
 
  private:
   friend class AstStorage;
@@ -2849,6 +2850,7 @@ class AuthQuery : public memgraph::query::Query {
     TRANSACTION_MANAGEMENT,
     MULTI_DATABASE_EDIT,
     MULTI_DATABASE_USE,
+    COORDINATOR
   };
 
   enum class FineGrainedPrivilege { NOTHING, READ, UPDATE, CREATE_DELETE };
@@ -2927,7 +2929,8 @@ const std::vector<AuthQuery::Privilege> kPrivilegesAll = {AuthQuery::Privilege::
                                                           AuthQuery::Privilege::TRANSACTION_MANAGEMENT,
                                                           AuthQuery::Privilege::STORAGE_MODE,
                                                           AuthQuery::Privilege::MULTI_DATABASE_EDIT,
-                                                          AuthQuery::Privilege::MULTI_DATABASE_USE};
+                                                          AuthQuery::Privilege::MULTI_DATABASE_USE,
+                                                          AuthQuery::Privilege::COORDINATOR};
 
 class DatabaseInfoQuery : public memgraph::query::Query {
  public:
@@ -3039,8 +3042,9 @@ class ReplicationQuery : public memgraph::query::Query {
 
   memgraph::query::ReplicationQuery::Action action_;
   memgraph::query::ReplicationQuery::ReplicationRole role_;
-  std::string replica_name_;
+  std::string instance_name_;
   memgraph::query::Expression *socket_address_{nullptr};
+  memgraph::query::Expression *coordinator_socket_address_{nullptr};
   memgraph::query::Expression *port_{nullptr};
   memgraph::query::ReplicationQuery::SyncMode sync_mode_;
 
@@ -3048,10 +3052,53 @@ class ReplicationQuery : public memgraph::query::Query {
     ReplicationQuery *object = storage->Create<ReplicationQuery>();
     object->action_ = action_;
     object->role_ = role_;
-    object->replica_name_ = replica_name_;
+    object->instance_name_ = instance_name_;
     object->socket_address_ = socket_address_ ? socket_address_->Clone(storage) : nullptr;
     object->port_ = port_ ? port_->Clone(storage) : nullptr;
     object->sync_mode_ = sync_mode_;
+    object->coordinator_socket_address_ =
+        coordinator_socket_address_ ? coordinator_socket_address_->Clone(storage) : nullptr;
+
+    return object;
+  }
+
+ private:
+  friend class AstStorage;
+};
+
+class CoordinatorQuery : public memgraph::query::Query {
+ public:
+  static const utils::TypeInfo kType;
+  const utils::TypeInfo &GetTypeInfo() const override { return kType; }
+
+  enum class Action {
+    REGISTER_INSTANCE,
+    SET_INSTANCE_TO_MAIN,
+    SHOW_REPLICATION_CLUSTER,
+  };
+
+  enum class SyncMode { SYNC, ASYNC };
+
+  CoordinatorQuery() = default;
+
+  DEFVISITABLE(QueryVisitor<void>);
+
+  memgraph::query::CoordinatorQuery::Action action_;
+  std::string instance_name_;
+  memgraph::query::Expression *replication_socket_address_{nullptr};
+  memgraph::query::Expression *coordinator_socket_address_{nullptr};
+  memgraph::query::CoordinatorQuery::SyncMode sync_mode_;
+
+  CoordinatorQuery *Clone(AstStorage *storage) const override {
+    auto *object = storage->Create<CoordinatorQuery>();
+    object->action_ = action_;
+    object->instance_name_ = instance_name_;
+    object->replication_socket_address_ =
+        replication_socket_address_ ? replication_socket_address_->Clone(storage) : nullptr;
+    object->sync_mode_ = sync_mode_;
+    object->coordinator_socket_address_ =
+        coordinator_socket_address_ ? coordinator_socket_address_->Clone(storage) : nullptr;
+
     return object;
   }
 
@@ -3612,7 +3659,7 @@ class MultiDatabaseQuery : public memgraph::query::Query {
 
   DEFVISITABLE(QueryVisitor<void>);
 
-  enum class Action { CREATE, USE, DROP };
+  enum class Action { CREATE, USE, DROP, SHOW };
 
   memgraph::query::MultiDatabaseQuery::Action action_;
   std::string db_name_;

src/query/frontend/ast/ast_visitor.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -108,6 +108,7 @@ class MultiDatabaseQuery;
 class ShowDatabasesQuery;
 class EdgeImportModeQuery;
 class PatternComprehension;
+class CoordinatorQuery;
 
 using TreeCompositeVisitor = utils::CompositeVisitor<
     SingleQuery, CypherUnion, NamedExpression, OrOperator, XorOperator, AndOperator, NotOperator, AdditionOperator,
@@ -146,6 +147,7 @@ class QueryVisitor
                             SystemInfoQuery, ConstraintQuery, DumpQuery, ReplicationQuery, LockPathQuery,
                             FreeMemoryQuery, TriggerQuery, IsolationLevelQuery, CreateSnapshotQuery, StreamQuery,
                             SettingQuery, VersionQuery, ShowConfigQuery, TransactionQueueQuery, StorageModeQuery,
-                            AnalyzeGraphQuery, MultiDatabaseQuery, ShowDatabasesQuery, EdgeImportModeQuery> {};
+                            AnalyzeGraphQuery, MultiDatabaseQuery, ShowDatabasesQuery, EdgeImportModeQuery,
+                            CoordinatorQuery> {};
 
 }  // namespace memgraph::query

src/query/frontend/ast/cypher_main_visitor.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -302,6 +302,13 @@ antlrcpp::Any CypherMainVisitor::visitReplicationQuery(MemgraphCypher::Replicati
   return replication_query;
 }
 
+antlrcpp::Any CypherMainVisitor::visitCoordinatorQuery(MemgraphCypher::CoordinatorQueryContext *ctx) {
+  MG_ASSERT(ctx->children.size() == 1, "CoordinatorQuery should have exactly one child!");
+  auto *coordinator_query = std::any_cast<CoordinatorQuery *>(ctx->children[0]->accept(this));
+  query_ = coordinator_query;
+  return coordinator_query;
+}
+
 antlrcpp::Any CypherMainVisitor::visitEdgeImportModeQuery(MemgraphCypher::EdgeImportModeQueryContext *ctx) {
   auto *edge_import_mode_query = storage_->Create<EdgeImportModeQuery>();
   if (ctx->ACTIVE()) {
@@ -316,24 +323,34 @@ antlrcpp::Any CypherMainVisitor::visitEdgeImportModeQuery(MemgraphCypher::EdgeIm
 antlrcpp::Any CypherMainVisitor::visitSetReplicationRole(MemgraphCypher::SetReplicationRoleContext *ctx) {
   auto *replication_query = storage_->Create<ReplicationQuery>();
   replication_query->action_ = ReplicationQuery::Action::SET_REPLICATION_ROLE;
+
+  auto set_replication_port = [replication_query, ctx, this]() -> void {
+    if (ctx->port->numberLiteral() && ctx->port->numberLiteral()->integerLiteral()) {
+      replication_query->port_ = std::any_cast<Expression *>(ctx->port->accept(this));
+    } else {
+      throw SyntaxException("Port must be an integer literal!");
+    }
+  };
+
   if (ctx->MAIN()) {
+    replication_query->role_ = ReplicationQuery::ReplicationRole::MAIN;
     if (ctx->WITH() || ctx->PORT()) {
       throw SemanticException("Main can't set a port!");
     }
-    replication_query->role_ = ReplicationQuery::ReplicationRole::MAIN;
+
   } else if (ctx->REPLICA()) {
     replication_query->role_ = ReplicationQuery::ReplicationRole::REPLICA;
     if (ctx->WITH() && ctx->PORT()) {
-      if (ctx->port->numberLiteral() && ctx->port->numberLiteral()->integerLiteral()) {
-        replication_query->port_ = std::any_cast<Expression *>(ctx->port->accept(this));
-      } else {
-        throw SyntaxException("Port must be an integer literal!");
-      }
+      set_replication_port();
+    } else {
+      throw SemanticException("Replica must set a port!");
     }
   }
+
   return replication_query;
 }
-antlrcpp::Any CypherMainVisitor::visitShowReplicationRole(MemgraphCypher::ShowReplicationRoleContext *ctx) {
+
+antlrcpp::Any CypherMainVisitor::visitShowReplicationRole(MemgraphCypher::ShowReplicationRoleContext * /*ctx*/) {
   auto *replication_query = storage_->Create<ReplicationQuery>();
   replication_query->action_ = ReplicationQuery::Action::SHOW_REPLICATION_ROLE;
   return replication_query;
@@ -342,7 +359,7 @@ antlrcpp::Any CypherMainVisitor::visitShowReplicationRole(MemgraphCypher::ShowRe
 antlrcpp::Any CypherMainVisitor::visitRegisterReplica(MemgraphCypher::RegisterReplicaContext *ctx) {
   auto *replication_query = storage_->Create<ReplicationQuery>();
   replication_query->action_ = ReplicationQuery::Action::REGISTER_REPLICA;
-  replication_query->replica_name_ = std::any_cast<std::string>(ctx->replicaName()->symbolicName()->accept(this));
+  replication_query->instance_name_ = std::any_cast<std::string>(ctx->instanceName()->symbolicName()->accept(this));
   if (ctx->SYNC()) {
     replication_query->sync_mode_ = memgraph::query::ReplicationQuery::SyncMode::SYNC;
   } else if (ctx->ASYNC()) {
@@ -351,26 +368,67 @@ antlrcpp::Any CypherMainVisitor::visitRegisterReplica(MemgraphCypher::RegisterRe
 
   if (!ctx->socketAddress()->literal()->StringLiteral()) {
     throw SemanticException("Socket address should be a string literal!");
-  } else {
-    replication_query->socket_address_ = std::any_cast<Expression *>(ctx->socketAddress()->accept(this));
   }
+  replication_query->socket_address_ = std::any_cast<Expression *>(ctx->socketAddress()->accept(this));
 
   return replication_query;
 }
 
+// License check is done in the interpreter.
+antlrcpp::Any CypherMainVisitor::visitRegisterInstanceOnCoordinator(
+    MemgraphCypher::RegisterInstanceOnCoordinatorContext *ctx) {
+  auto *coordinator_query = storage_->Create<CoordinatorQuery>();
+  if (!ctx->replicationSocketAddress()->literal()->StringLiteral()) {
+    throw SemanticException("Replication socket address should be a string literal!");
+  }
+
+  if (!ctx->coordinatorSocketAddress()->literal()->StringLiteral()) {
+    throw SemanticException("Coordinator socket address should be a string literal!");
+  }
+  coordinator_query->action_ = CoordinatorQuery::Action::REGISTER_INSTANCE;
+  coordinator_query->replication_socket_address_ =
+      std::any_cast<Expression *>(ctx->replicationSocketAddress()->accept(this));
+  coordinator_query->coordinator_socket_address_ =
+      std::any_cast<Expression *>(ctx->coordinatorSocketAddress()->accept(this));
+  coordinator_query->instance_name_ = std::any_cast<std::string>(ctx->instanceName()->symbolicName()->accept(this));
+  if (ctx->ASYNC()) {
+    coordinator_query->sync_mode_ = memgraph::query::CoordinatorQuery::SyncMode::ASYNC;
+  } else {
+    coordinator_query->sync_mode_ = memgraph::query::CoordinatorQuery::SyncMode::SYNC;
+  }
+
+  return coordinator_query;
+}
+
+// License check is done in the interpreter
+antlrcpp::Any CypherMainVisitor::visitShowReplicationCluster(MemgraphCypher::ShowReplicationClusterContext * /*ctx*/) {
+  auto *coordinator_query = storage_->Create<CoordinatorQuery>();
+  coordinator_query->action_ = CoordinatorQuery::Action::SHOW_REPLICATION_CLUSTER;
+  return coordinator_query;
+}
+
 antlrcpp::Any CypherMainVisitor::visitDropReplica(MemgraphCypher::DropReplicaContext *ctx) {
   auto *replication_query = storage_->Create<ReplicationQuery>();
   replication_query->action_ = ReplicationQuery::Action::DROP_REPLICA;
-  replication_query->replica_name_ = std::any_cast<std::string>(ctx->replicaName()->symbolicName()->accept(this));
+  replication_query->instance_name_ = std::any_cast<std::string>(ctx->instanceName()->symbolicName()->accept(this));
   return replication_query;
 }
 
-antlrcpp::Any CypherMainVisitor::visitShowReplicas(MemgraphCypher::ShowReplicasContext *ctx) {
+antlrcpp::Any CypherMainVisitor::visitShowReplicas(MemgraphCypher::ShowReplicasContext * /*ctx*/) {
   auto *replication_query = storage_->Create<ReplicationQuery>();
   replication_query->action_ = ReplicationQuery::Action::SHOW_REPLICAS;
   return replication_query;
 }
 
+// License check is done in the interpreter
+antlrcpp::Any CypherMainVisitor::visitSetInstanceToMain(MemgraphCypher::SetInstanceToMainContext *ctx) {
+  auto *coordinator_query = storage_->Create<CoordinatorQuery>();
+  coordinator_query->action_ = CoordinatorQuery::Action::SET_INSTANCE_TO_MAIN;
+  coordinator_query->instance_name_ = std::any_cast<std::string>(ctx->instanceName()->symbolicName()->accept(this));
+  query_ = coordinator_query;
+  return coordinator_query;
+}
+
 antlrcpp::Any CypherMainVisitor::visitLockPathQuery(MemgraphCypher::LockPathQueryContext *ctx) {
   auto *lock_query = storage_->Create<LockPathQuery>();
   if (ctx->STATUS()) {
@@ -1638,6 +1696,7 @@ antlrcpp::Any CypherMainVisitor::visitPrivilege(MemgraphCypher::PrivilegeContext
   if (ctx->STORAGE_MODE()) return AuthQuery::Privilege::STORAGE_MODE;
   if (ctx->MULTI_DATABASE_EDIT()) return AuthQuery::Privilege::MULTI_DATABASE_EDIT;
   if (ctx->MULTI_DATABASE_USE()) return AuthQuery::Privilege::MULTI_DATABASE_USE;
+  if (ctx->COORDINATOR()) return AuthQuery::Privilege::COORDINATOR;
   LOG_FATAL("Should not get here - unknown privilege!");
 }
 
@@ -1752,7 +1811,11 @@ antlrcpp::Any CypherMainVisitor::visitReturnBody(MemgraphCypher::ReturnBodyConte
     body.skip = static_cast<Expression *>(std::any_cast<Expression *>(ctx->skip()->accept(this)));
   }
   if (ctx->limit()) {
-    body.limit = static_cast<Expression *>(std::any_cast<Expression *>(ctx->limit()->accept(this)));
+    if (ctx->limit()->expression()) {
+      body.limit = std::any_cast<Expression *>(ctx->limit()->accept(this));
+    } else {
+      body.limit = std::any_cast<ParameterLookup *>(ctx->limit()->accept(this));
+    }
   }
   std::tie(body.all_identifiers, body.named_expressions) =
       std::any_cast<std::pair<bool, std::vector<NamedExpression *>>>(ctx->returnItems()->accept(this));
@@ -2888,6 +2951,14 @@ antlrcpp::Any CypherMainVisitor::visitDropDatabase(MemgraphCypher::DropDatabaseC
   return mdb_query;
 }
 
+antlrcpp::Any CypherMainVisitor::visitShowDatabase(MemgraphCypher::ShowDatabaseContext * /*ctx*/) {
+  auto *mdb_query = storage_->Create<MultiDatabaseQuery>();
+  mdb_query->db_name_ = "";
+  mdb_query->action_ = MultiDatabaseQuery::Action::SHOW;
+  query_ = mdb_query;
+  return mdb_query;
+}
+
 antlrcpp::Any CypherMainVisitor::visitShowDatabases(MemgraphCypher::ShowDatabasesContext * /*ctx*/) {
   query_ = storage_->Create<ShowDatabasesQuery>();
   return query_;

src/query/frontend/ast/cypher_main_visitor.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -233,6 +233,26 @@ class CypherMainVisitor : public antlropencypher::MemgraphCypherBaseVisitor {
    */
   antlrcpp::Any visitShowReplicas(MemgraphCypher::ShowReplicasContext *ctx) override;
 
+  /**
+   * @return CoordinatorQuery*
+   */
+  antlrcpp::Any visitCoordinatorQuery(MemgraphCypher::CoordinatorQueryContext *ctx) override;
+
+  /**
+   * @return CoordinatorQuery*
+   */
+  antlrcpp::Any visitRegisterInstanceOnCoordinator(MemgraphCypher::RegisterInstanceOnCoordinatorContext *ctx) override;
+
+  /**
+   * @return CoordinatorQuery*
+   */
+  antlrcpp::Any visitSetInstanceToMain(MemgraphCypher::SetInstanceToMainContext *ctx) override;
+
+  /**
+   * @return CoordinatorQuery*
+   */
+  antlrcpp::Any visitShowReplicationCluster(MemgraphCypher::ShowReplicationClusterContext *ctx) override;
+
   /**
    * @return LockPathQuery*
    */
@@ -997,6 +1017,11 @@ class CypherMainVisitor : public antlropencypher::MemgraphCypherBaseVisitor {
    */
   antlrcpp::Any visitDropDatabase(MemgraphCypher::DropDatabaseContext *ctx) override;
 
+  /**
+   * @return MultiDatabaseQuery*
+   */
+  antlrcpp::Any visitShowDatabase(MemgraphCypher::ShowDatabaseContext *ctx) override;
+
   /**
    * @return ShowDatabasesQuery*
    */

src/query/frontend/opencypher/grammar/Cypher.g4

@@ -143,7 +143,7 @@ order : ORDER BY sortItem ( ',' sortItem )* ;
 
 skip : L_SKIP expression ;
 
-limit : LIMIT expression ;
+limit : LIMIT ( expression | parameter ) ;
 
 sortItem : expression ( ASCENDING | ASC | DESCENDING | DESC )? ;
 

src/query/frontend/opencypher/grammar/CypherLexer.g4

@@ -102,6 +102,7 @@ FILTER         : F I L T E R ;
 IN             : I N ;
 INDEX          : I N D E X ;
 INFO           : I N F O ;
+INSTANCE       : I N S T A N C E ;
 IS             : I S ;
 KB             : K B ;
 KEY            : K E Y ;
@@ -122,6 +123,7 @@ PROCEDURE      : P R O C E D U R E ;
 PROFILE        : P R O F I L E ;
 QUERY          : Q U E R Y ;
 REDUCE         : R E D U C E ;
+REGISTER       : R E G I S T E R;
 REMOVE         : R E M O V E ;
 RETURN         : R E T U R N ;
 SET            : S E T ;

src/query/frontend/opencypher/grammar/MemgraphCypher.g4

@@ -48,10 +48,12 @@ memgraphCypherKeyword : cypherKeyword
                       | DATABASE
                       | DENY
                       | DROP
+                      | DO
                       | DUMP
                       | EDGE
                       | EDGE_TYPES
                       | EXECUTE
+                      | FAILOVER
                       | FOR
                       | FOREACH
                       | FREE
@@ -61,6 +63,7 @@ memgraphCypherKeyword : cypherKeyword
                       | GRANT
                       | HEADER
                       | IDENTIFIED
+                      | INSTANCE
                       | NODE_LABELS
                       | NULLIF
                       | IMPORT
@@ -151,6 +154,7 @@ query : cypherQuery
       | multiDatabaseQuery
       | showDatabases
       | edgeImportModeQuery
+      | coordinatorQuery
       ;
 
 cypherQuery : ( indexHints )? singleQuery ( cypherUnion )* ( queryMemoryLimit )? ;
@@ -183,6 +187,11 @@ replicationQuery : setReplicationRole
                  | showReplicas
                  ;
 
+coordinatorQuery : registerInstanceOnCoordinator
+                 | setInstanceToMain
+                 | showReplicationCluster
+                 ;
+
 triggerQuery : createTrigger
              | dropTrigger
              | showTriggers
@@ -323,6 +332,7 @@ privilege : CREATE
           | STORAGE_MODE
           | MULTI_DATABASE_EDIT
           | MULTI_DATABASE_USE
+          | COORDINATOR
           ;
 
 granularPrivilege : NOTHING | READ | UPDATE | CREATE_DELETE ;
@@ -364,14 +374,23 @@ setReplicationRole : SET REPLICATION ROLE TO ( MAIN | REPLICA )
 
 showReplicationRole : SHOW REPLICATION ROLE ;
 
-replicaName : symbolicName ;
+showReplicationCluster : SHOW REPLICATION CLUSTER ;
+
+instanceName : symbolicName ;
 
 socketAddress : literal ;
 
-registerReplica : REGISTER REPLICA replicaName ( SYNC | ASYNC )
+coordinatorSocketAddress : literal ;
+replicationSocketAddress : literal ;
+
+registerReplica : REGISTER REPLICA instanceName ( SYNC | ASYNC )
                 TO socketAddress ;
 
-dropReplica : DROP REPLICA replicaName ;
+registerInstanceOnCoordinator : REGISTER INSTANCE instanceName ON coordinatorSocketAddress ( AS ASYNC ) ? WITH replicationSocketAddress ;
+
+setInstanceToMain : SET INSTANCE instanceName TO MAIN ;
+
+dropReplica : DROP REPLICA instanceName ;
 
 showReplicas : SHOW REPLICAS ;
 
@@ -480,6 +499,7 @@ transactionId : literal ;
 multiDatabaseQuery : createDatabase
                    | useDatabase
                    | dropDatabase
+                   | showDatabase
                    ;
 
 createDatabase : CREATE DATABASE databaseName ;
@@ -488,6 +508,8 @@ useDatabase : USE DATABASE databaseName ;
 
 dropDatabase : DROP DATABASE databaseName ;
 
+showDatabase : SHOW DATABASE ;
+
 showDatabases : SHOW DATABASES ;
 
 edgeImportModeQuery : EDGE IMPORT MODE ( ACTIVE | INACTIVE ) ;

src/query/frontend/opencypher/grammar/MemgraphCypherLexer.g4

@@ -39,15 +39,18 @@ BOOTSTRAP_SERVERS       : B O O T S T R A P UNDERSCORE S E R V E R S ;
 CALL                    : C A L L ;
 CHECK                   : C H E C K ;
 CLEAR                   : C L E A R ;
+CLUSTER                 : C L U S T E R ;
 COMMIT                  : C O M M I T ;
 COMMITTED               : C O M M I T T E D ;
 CONFIG                  : C O N F I G ;
 CONFIGS                 : C O N F I G S;
 CONSUMER_GROUP          : C O N S U M E R UNDERSCORE G R O U P ;
+COORDINATOR             : C O O R D I N A T O R ;
 CREATE_DELETE           : C R E A T E UNDERSCORE D E L E T E ;
 CREDENTIALS             : C R E D E N T I A L S ;
 CSV                     : C S V ;
 DATA                    : D A T A ;
+DO                      : D O ;
 DELIMITER               : D E L I M I T E R ;
 DATABASE                : D A T A B A S E ;
 DATABASES               : D A T A B A S E S ;
@@ -59,6 +62,7 @@ DURABILITY              : D U R A B I L I T Y ;
 EDGE                    : E D G E ;
 EDGE_TYPES              : E D G E UNDERSCORE T Y P E S ;
 EXECUTE                 : E X E C U T E ;
+FAILOVER                : F A I L O V E R ;
 FOR                     : F O R ;
 FOREACH                 : F O R E A C H;
 FREE                    : F R E E ;
@@ -75,6 +79,7 @@ IMPORT                  : I M P O R T ;
 INACTIVE                : I N A C T I V E ;
 IN_MEMORY_ANALYTICAL    : I N UNDERSCORE M E M O R Y UNDERSCORE A N A L Y T I C A L ;
 IN_MEMORY_TRANSACTIONAL : I N UNDERSCORE M E M O R Y UNDERSCORE T R A N S A C T I O N A L ;
+INSTANCE                : I N S T A N C E ;
 ISOLATION               : I S O L A T I O N ;
 KAFKA                   : K A F K A ;
 LABELS                  : L A B E L S ;
@@ -107,6 +112,7 @@ REVOKE                  : R E V O K E ;
 ROLE                    : R O L E ;
 ROLES                   : R O L E S ;
 QUOTE                   : Q U O T E ;
+SERVER                  : S E R V E R ;
 SERVICE_URL             : S E R V I C E UNDERSCORE U R L ;
 SESSION                 : S E S S I O N ;
 SETTING                 : S E T T I N G ;

src/query/frontend/semantic/required_privileges.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -106,6 +106,7 @@ class PrivilegeExtractor : public QueryVisitor<void>, public HierarchicalTreeVis
         AddPrivilege(AuthQuery::Privilege::MULTI_DATABASE_EDIT);
         break;
       case MultiDatabaseQuery::Action::USE:
+      case MultiDatabaseQuery::Action::SHOW:
         AddPrivilege(AuthQuery::Privilege::MULTI_DATABASE_USE);
         break;
     }
@@ -115,6 +116,8 @@ class PrivilegeExtractor : public QueryVisitor<void>, public HierarchicalTreeVis
     AddPrivilege(AuthQuery::Privilege::MULTI_DATABASE_USE); /* OR EDIT */
   }
 
+  void Visit(CoordinatorQuery & /*coordinator_query*/) override { AddPrivilege(AuthQuery::Privilege::COORDINATOR); }
+
   bool PreVisit(Create & /*unused*/) override {
     AddPrivilege(AuthQuery::Privilege::CREATE);
     return false;

src/query/frontend/stripped_lexer_constants.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -218,7 +218,8 @@ const trie::Trie kKeywords = {"union",
                               "directory",
                               "lock",
                               "unlock",
-                              "build"};
+                              "build",
+                              "instance"};
 
 // Unicode codepoints that are allowed at the start of the unescaped name.
 const std::bitset<kBitsetSize> kUnescapedNameAllowedStarts(

src/query/interpret/eval.hpp

@@ -1121,11 +1121,11 @@ class ExpressionEvaluator : public ExpressionVisitor<TypedValue> {
           throw QueryRuntimeException("Unexpected error when getting properties.");
       }
     }
-    return *maybe_props;
+    return *std::move(maybe_props);
   }
 
   template <class TRecordAccessor>
-  storage::PropertyValue GetProperty(const TRecordAccessor &record_accessor, PropertyIx prop) {
+  storage::PropertyValue GetProperty(const TRecordAccessor &record_accessor, const PropertyIx &prop) {
     auto maybe_prop = record_accessor.GetProperty(view_, ctx_->properties[prop.ix]);
     if (maybe_prop.HasError() && maybe_prop.GetError() == storage::Error::NONEXISTENT_OBJECT) {
       // This is a very nasty and temporary hack in order to make MERGE work.
@@ -1148,7 +1148,7 @@ class ExpressionEvaluator : public ExpressionVisitor<TypedValue> {
           throw QueryRuntimeException("Unexpected error when getting a property.");
       }
     }
-    return *maybe_prop;
+    return *std::move(maybe_prop);
   }
 
   template <class TRecordAccessor>
@@ -1178,7 +1178,7 @@ class ExpressionEvaluator : public ExpressionVisitor<TypedValue> {
     return *maybe_prop;
   }
 
-  storage::LabelId GetLabel(LabelIx label) { return ctx_->labels[label.ix]; }
+  storage::LabelId GetLabel(const LabelIx &label) { return ctx_->labels[label.ix]; }
 
   Frame *frame_;
   const SymbolTable *symbol_table_;

src/query/interpreter.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -16,6 +16,7 @@
 #include <gflags/gflags.h>
 
 #include "dbms/database.hpp"
+#include "dbms/dbms_handler.hpp"
 #include "memory/query_memory_control.hpp"
 #include "query/auth_checker.hpp"
 #include "query/auth_query_handler.hpp"
@@ -51,6 +52,10 @@
 #include "utils/timer.hpp"
 #include "utils/tsc.hpp"
 
+#ifdef MG_ENTERPRISE
+#include "coordination/coordinator_instance_status.hpp"
+#endif
+
 namespace memgraph::metrics {
 extern const Event FailedQuery;
 extern const Event FailedPrepare;
@@ -67,16 +72,16 @@ inline constexpr size_t kExecutionPoolMaxBlockSize = 1024UL;  // 2 ^ 10
 
 enum class QueryHandlerResult { COMMIT, ABORT, NOTHING };
 
-class ReplicationQueryHandler {
+class CoordinatorQueryHandler {
  public:
-  ReplicationQueryHandler() = default;
-  virtual ~ReplicationQueryHandler() = default;
+  CoordinatorQueryHandler() = default;
+  virtual ~CoordinatorQueryHandler() = default;
 
-  ReplicationQueryHandler(const ReplicationQueryHandler &) = default;
-  ReplicationQueryHandler &operator=(const ReplicationQueryHandler &) = default;
+  CoordinatorQueryHandler(const CoordinatorQueryHandler &) = default;
+  CoordinatorQueryHandler &operator=(const CoordinatorQueryHandler &) = default;
 
-  ReplicationQueryHandler(ReplicationQueryHandler &&) = default;
-  ReplicationQueryHandler &operator=(ReplicationQueryHandler &&) = default;
+  CoordinatorQueryHandler(CoordinatorQueryHandler &&) = default;
+  CoordinatorQueryHandler &operator=(CoordinatorQueryHandler &&) = default;
 
   struct Replica {
     std::string name;
@@ -88,22 +93,32 @@ class ReplicationQueryHandler {
     ReplicationQuery::ReplicaState state;
   };
 
+#ifdef MG_ENTERPRISE
+  struct MainReplicaStatus {
+    std::string_view name;
+    std::string_view socket_address;
+    bool alive;
+    bool is_main;
+
+    MainReplicaStatus(std::string_view name, std::string_view socket_address, bool alive, bool is_main)
+        : name{name}, socket_address{socket_address}, alive{alive}, is_main{is_main} {}
+  };
+#endif
+
+#ifdef MG_ENTERPRISE
   /// @throw QueryRuntimeException if an error ocurred.
-  virtual void SetReplicationRole(ReplicationQuery::ReplicationRole replication_role, std::optional<int64_t> port) = 0;
+  virtual void RegisterInstance(const std::string &coordinator_socket_address,
+                                const std::string &replication_socket_address,
+                                const std::chrono::seconds instance_check_frequency, const std::string &instance_name,
+                                CoordinatorQuery::SyncMode sync_mode) = 0;
 
   /// @throw QueryRuntimeException if an error ocurred.
-  virtual ReplicationQuery::ReplicationRole ShowReplicationRole() const = 0;
+  virtual void SetInstanceToMain(const std::string &instance_name) = 0;
 
   /// @throw QueryRuntimeException if an error ocurred.
-  virtual void RegisterReplica(const std::string &name, const std::string &socket_address,
-                               ReplicationQuery::SyncMode sync_mode,
-                               const std::chrono::seconds replica_check_frequency) = 0;
+  virtual std::vector<coordination::CoordinatorInstanceStatus> ShowInstances() const = 0;
 
-  /// @throw QueryRuntimeException if an error ocurred.
-  virtual void DropReplica(std::string_view replica_name) = 0;
-
-  /// @throw QueryRuntimeException if an error ocurred.
-  virtual std::vector<Replica> ShowReplicas() const = 0;
+#endif
 };
 
 class AnalyzeGraphQueryHandler {
@@ -281,7 +296,38 @@ class Interpreter final {
 
   void SetUser(std::string_view username);
 
+  struct SystemTransactionGuard {
+    explicit SystemTransactionGuard(std::unique_lock<utils::ResourceLock> guard, dbms::DbmsHandler &dbms_handler)
+        : system_guard_(std::move(guard)), dbms_handler_{&dbms_handler} {
+      dbms_handler_->NewSystemTransaction();
+    }
+    SystemTransactionGuard &operator=(SystemTransactionGuard &&) = default;
+    SystemTransactionGuard(SystemTransactionGuard &&) = default;
+
+    ~SystemTransactionGuard() {
+      if (system_guard_.owns_lock()) dbms_handler_->ResetSystemTransaction();
+    }
+
+    dbms::AllSyncReplicaStatus Commit() { return dbms_handler_->Commit(); }
+
+   private:
+    std::unique_lock<utils::ResourceLock> system_guard_;
+    dbms::DbmsHandler *dbms_handler_;
+  };
+
+  std::optional<SystemTransactionGuard> system_transaction_guard_{};
+
  private:
+  void ResetInterpreter() {
+    query_executions_.clear();
+    system_guard.reset();
+    system_transaction_guard_.reset();
+    transaction_queries_->clear();
+    if (current_db_.db_acc_ && current_db_.db_acc_->is_deleting()) {
+      current_db_.db_acc_.reset();
+    }
+  }
+
   struct QueryExecution {
     std::variant<utils::MonotonicBufferResource, utils::PoolResource> execution_memory;
     utils::ResourceWithOutOfMemoryException execution_memory_with_exception;
@@ -340,6 +386,9 @@ class Interpreter final {
   // TODO Figure out how this would work for multi-database
   // Exists only during a single transaction (for now should be okay as is)
   std::vector<std::unique_ptr<QueryExecution>> query_executions_;
+  // TODO: our upgradable lock guard for system
+  std::optional<utils::ResourceLockGuard> system_guard;
+
   // all queries that are run as part of the current transaction
   utils::Synchronized<std::vector<std::string>, utils::SpinLock> transaction_queries_;
 
@@ -435,8 +484,7 @@ std::map<std::string, TypedValue> Interpreter::Pull(TStream *result_stream, std:
         // NOTE: we cannot clear query_execution inside the Abort and Commit
         // methods as we will delete summary contained in them which we need
         // after our query finished executing.
-        query_executions_.clear();
-        transaction_queries_->clear();
+        ResetInterpreter();
       } else {
         // We can only clear this execution as some of the queries
         // in the transaction can be in unfinished state

src/query/interpreter_context.cpp

@@ -56,7 +56,7 @@ std::vector<std::vector<TypedValue>> InterpreterContext::TerminateTransactions(
         std::iter_swap(it, not_found_midpoint);
         auto get_interpreter_db_name = [&]() -> std::string const & {
           static std::string all;
-          return interpreter->current_db_.db_acc_ ? interpreter->current_db_.db_acc_->get()->id() : all;
+          return interpreter->current_db_.db_acc_ ? interpreter->current_db_.db_acc_->get()->name() : all;
         };
         if (interpreter->username_ == username || privilege_checker(get_interpreter_db_name())) {
           killed = true;  // Note: this is used by the above `clean_status` (OnScopeExit)

src/query/interpreter_context.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -22,6 +22,8 @@
 #include "query/cypher_query_interpreter.hpp"
 #include "query/typed_value.hpp"
 #include "replication/state.hpp"
+#include "storage/v2/config.hpp"
+#include "storage/v2/transaction.hpp"
 #include "utils/gatekeeper.hpp"
 #include "utils/skip_list.hpp"
 #include "utils/spin_lock.hpp"
@@ -57,6 +59,7 @@ struct InterpreterContext {
 
   // GLOBAL
   memgraph::replication::ReplicationState *repl_state;
+
   AuthQueryHandler *auth;
   AuthChecker *auth_checker;
 

src/query/metadata.cpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -66,6 +66,10 @@ constexpr std::string_view GetCodeString(const NotificationCode code) {
       return "PlanHinting"sv;
     case NotificationCode::REGISTER_REPLICA:
       return "RegisterReplica"sv;
+#ifdef MG_ENTERPRISE
+    case NotificationCode::REGISTER_COORDINATOR_SERVER:
+      return "RegisterCoordinatorServer"sv;
+#endif
     case NotificationCode::REPLICA_PORT_WARNING:
       return "ReplicaPortWarning"sv;
     case NotificationCode::SET_REPLICA:

src/query/metadata.hpp

@@ -1,4 +1,4 @@
-// Copyright 2023 Memgraph Ltd.
+// Copyright 2024 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -42,6 +42,9 @@ enum class NotificationCode : uint8_t {
   PLAN_HINTING,
   REPLICA_PORT_WARNING,
   REGISTER_REPLICA,
+#ifdef MG_ENTERPRISE
+  REGISTER_COORDINATOR_SERVER,
+#endif
   SET_REPLICA,
   START_STREAM,
   START_ALL_STREAMS,

src/query/plan/operator.hpp

@@ -916,11 +916,11 @@ struct ExpansionLambda {
   /// Currently expanded node symbol.
   Symbol inner_node_symbol;
   /// Expression used in lambda during expansion.
-  Expression *expression;
+  Expression *expression = nullptr;
   /// Currently expanded accumulated path symbol.
-  std::optional<Symbol> accumulated_path_symbol;
+  std::optional<Symbol> accumulated_path_symbol = std::nullopt;
   /// Currently expanded accumulated weight symbol.
-  std::optional<Symbol> accumulated_weight_symbol;
+  std::optional<Symbol> accumulated_weight_symbol = std::nullopt;
 
   ExpansionLambda Clone(AstStorage *storage) const {
     ExpansionLambda object;