filer: optimization for leveldb, add leveldb2

large filer db may see high CPU and disk usage due to background compaction

weed/filer2/leveldb/leveldb_store.go

@@ -9,6 +9,7 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	weed_util "github.com/chrislusf/seaweedfs/weed/util"
 	"github.com/syndtr/goleveldb/leveldb"
+	"github.com/syndtr/goleveldb/leveldb/opt"
 	leveldb_util "github.com/syndtr/goleveldb/leveldb/util"
 )
 
@@ -39,7 +40,13 @@ func (store *LevelDBStore) initialize(dir string) (err error) {
 		return fmt.Errorf("Check Level Folder %s Writable: %s", dir, err)
 	}
 
-	if store.db, err = leveldb.OpenFile(dir, nil); err != nil {
+	opts := &opt.Options{
+		BlockCacheCapacity:            32 * 1024 * 1024, // default value is 8MiB
+		WriteBuffer:                   16 * 1024 * 1024, // default value is 4MiB
+		CompactionTableSizeMultiplier: 4,
+	}
+
+	if store.db, err = leveldb.OpenFile(dir, opts); err != nil {
 		glog.Infof("filer store open dir %s: %v", dir, err)
 		return
 	}