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何卓然
2021-01-04 10:25:36 +08:00
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doc/project1-StandaloneKV.md
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# Project1 StandaloneKV
In this project, you will build a standalone key/value storage [gRPC](https://grpc.io/docs/guides/) service with the support of column family. Standalone means only a single node, not a distributed system. Column family( <https://en.wikipedia.org/wiki/Standard_column_family> , it will abbreviate to CF below) is a term like key namespace, namely the values of the same key in different column families is not the same. You can simply regard multiple column families as separate mini databases. It’s used to support the transaction model in project4, you will know why TinyKV needs the support of CF then.
In this project, you will build a standalone key/value storage [gRPC](https://grpc.io/docs/guides/) service with the support of the column family. Standalone means only a single node, not a distributed system. [Column family]( <https://en.wikipedia.org/wiki/Standard_column_family> ), it will abbreviate to CF below) is a term like key namespace, namely the values of the same key in different column families is not the same. You can simply regard multiple column families as separate mini databases. It’s used to support the transaction model in the project4, you will know why TinyKV needs the support of CF then.
The service supports four basic operations: Put/Delete/Get/Scan. It maintains a simple database of key/value pairs. Keys and values are strings. `Put` replaces the value for a particular key for the specified CF in the database, `Delete` deletes the key's value for the specified CF, `Get` fetches the current value for a key for the specified CF, and `Scan` fetches the current value for a series of keys for the specified CF.
@@ -37,7 +37,7 @@ And you don’t need to consider the `kvrpcpb.Context` now, it’s used in the f
> Hints:
>
> - You should use [badger.Txn]( https://godoc.org/github.com/dgraph-io/badger#Txn ) to implement the `Reader` function, because the transcation handler provided by badger could provide a consistent snapshot of the keys and values.
> - You should use [badger.Txn]( https://godoc.org/github.com/dgraph-io/badger#Txn ) to implement the `Reader` function because the transaction handler provided by badger could provide a consistent snapshot of the keys and values.
> - Badger doesn’t give support for column families. engine_util package (`kv/util/engine_util`) simulates column families by adding a prefix to keys. For example, a key `key` that belongs to a specific column family `cf` is stored as `${cf}_${key}`. It wraps `badger` to provide operations with CFs, and also offers many useful helper functions. So you should do all read/write operations through `engine_util` provided methods. Please read `util/engine_util/doc.go` to learn more.
> - TinyKV uses a fork of the original version of `badger` with some fix, so just use `github.com/Connor1996/badger` instead of `github.com/dgraph-io/badger`.
> - Don’t forget to call `Discard()` for badger.Txn and close all iterators before discarding.