A number of smaller fixes and performance improvements:

- Implemented Get() directly instead of building on top of a full
  merging iterator stack.  This speeds up the "readrandom" benchmark
  by up to 15-30%.

- Fixed an opensource compilation problem.
  Added --db=<name> flag to control where the database is placed.

- Automatically compact a file when we have done enough
  overlapping seeks to that file.

- Fixed a performance bug where we would read from at least one
  file in a level even if none of the files overlapped the key
  being read.

- Makefile fix for Mac OSX installations that have XCode 4 without XCode 3.

- Unified the two occurrences of binary search in a file-list
  into one routine.

- Found and fixed a bug where we would unnecessarily search the
  last file when looking for a key larger than all data in the
  level.

- A fix to avoid the need for trivial move compactions and
  therefore gets rid of two out of five syncs in "fillseq".

- Removed the MANIFEST file write when switching to a new
  memtable/log-file for a 10-20% improvement on fill speed on ext4.

- Adding a SNAPPY setting in the Makefile for folks who have
  Snappy installed. Snappy compresses values and speeds up writes.



git-svn-id: https://leveldb.googlecode.com/svn/trunk@32 62dab493-f737-651d-591e-8d6aee1b9529

db/db_bench.cc

@@ -86,6 +86,9 @@ static int FLAGS_open_files = 0;
 // benchmark will fail.
 static bool FLAGS_use_existing_db = false;
 
+// Use the db with the following name.
+static const char* FLAGS_db = "/tmp/dbbench";
+
 namespace leveldb {
 
 // Helper for quickly generating random data.
@@ -318,14 +321,14 @@ class Benchmark {
     bytes_(0),
     rand_(301) {
     std::vector<std::string> files;
-    Env::Default()->GetChildren("/tmp/dbbench", &files);
+    Env::Default()->GetChildren(FLAGS_db, &files);
     for (int i = 0; i < files.size(); i++) {
       if (Slice(files[i]).starts_with("heap-")) {
-        Env::Default()->DeleteFile("/tmp/dbbench/" + files[i]);
+        Env::Default()->DeleteFile(std::string(FLAGS_db) + "/" + files[i]);
       }
     }
     if (!FLAGS_use_existing_db) {
-      DestroyDB("/tmp/dbbench", Options());
+      DestroyDB(FLAGS_db, Options());
     }
   }
 
@@ -364,7 +367,7 @@ class Benchmark {
         Write(write_options, RANDOM, EXISTING, num_, FLAGS_value_size, 1);
       } else if (name == Slice("fillsync")) {
         write_options.sync = true;
-        Write(write_options, RANDOM, FRESH, num_ / 100, FLAGS_value_size, 1);
+        Write(write_options, RANDOM, FRESH, num_ / 1000, FLAGS_value_size, 1);
       } else if (name == Slice("fill100K")) {
         Write(write_options, RANDOM, FRESH, num_ / 1000, 100 * 1000, 1);
       } else if (name == Slice("readseq")) {
@@ -490,7 +493,7 @@ class Benchmark {
     options.create_if_missing = !FLAGS_use_existing_db;
     options.block_cache = cache_;
     options.write_buffer_size = FLAGS_write_buffer_size;
-    Status s = DB::Open(options, "/tmp/dbbench", &db_);
+    Status s = DB::Open(options, FLAGS_db, &db_);
     if (!s.ok()) {
       fprintf(stderr, "open error: %s\n", s.ToString().c_str());
       exit(1);
@@ -506,7 +509,7 @@ class Benchmark {
       }
       delete db_;
       db_ = NULL;
-      DestroyDB("/tmp/dbbench", Options());
+      DestroyDB(FLAGS_db, Options());
       Open();
       Start();  // Do not count time taken to destroy/open
     }
@@ -617,7 +620,7 @@ class Benchmark {
 
   void HeapProfile() {
     char fname[100];
-    snprintf(fname, sizeof(fname), "/tmp/dbbench/heap-%04d", ++heap_counter_);
+    snprintf(fname, sizeof(fname), "%s/heap-%04d", FLAGS_db, ++heap_counter_);
     WritableFile* file;
     Status s = Env::Default()->NewWritableFile(fname, &file);
     if (!s.ok()) {
@@ -665,6 +668,8 @@ int main(int argc, char** argv) {
       FLAGS_cache_size = n;
     } else if (sscanf(argv[i], "--open_files=%d%c", &n, &junk) == 1) {
       FLAGS_open_files = n;
+    } else if (strncmp(argv[i], "--db=", 5) == 0) {
+      FLAGS_db = argv[i] + 5;
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);