filer: optimization for leveldb, add leveldb2

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

unmaintained/compact_leveldb/compact_leveldb.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"flag"
+	"log"
+
+	"github.com/syndtr/goleveldb/leveldb"
+	"github.com/syndtr/goleveldb/leveldb/opt"
+	"github.com/syndtr/goleveldb/leveldb/util"
+)
+
+var (
+	dir = flag.String("dir", ".", "data directory to store leveldb files")
+)
+
+func main() {
+
+	flag.Parse()
+
+	opts := &opt.Options{
+		BlockCacheCapacity:            32 * 1024 * 1024, // default value is 8MiB
+		WriteBuffer:                   16 * 1024 * 1024, // default value is 4MiB
+		CompactionTableSizeMultiplier: 10,
+		OpenFilesCacheCapacity:        -1,
+	}
+
+	db, err := leveldb.OpenFile(*dir, opts)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer db.Close()
+	if err := db.CompactRange(util.Range{}); err != nil {
+		log.Fatal(err)
+	}
+}