add leveldb support for needle map

This supposedly should reduce memory consumption. However, for tests
with millions of, this shows consuming more memories. Need to see
whether this will work out. If not, later boltdb will be tested.

go/weed/server.go

@@ -68,6 +68,7 @@ var (
 	volumeDataFolders             = cmdServer.Flag.String("dir", os.TempDir(), "directories to store data files. dir[,dir]...")
 	volumeMaxDataVolumeCounts     = cmdServer.Flag.String("volume.max", "7", "maximum numbers of volumes, count[,count]...")
 	volumePulse                   = cmdServer.Flag.Int("pulseSeconds", 5, "number of seconds between heartbeats")
+	volumeUseLevelDb              = cmdServer.Flag.Bool("volume.leveldb", false, "Change to leveldb mode to save memory with reduced performance of read and write.")
 	volumeFixJpgOrientation       = cmdServer.Flag.Bool("volume.images.fix.orientation", true, "Adjust jpg orientation when uploading.")
 	isStartingFiler               = cmdServer.Flag.Bool("filer", false, "whether to start filer")
 
@@ -235,6 +236,7 @@ func runServer(cmd *Command, args []string) bool {
 	volumeServer := weed_server.NewVolumeServer(volumeMux, publicVolumeMux,
 		*serverIp, *volumePort, *serverPublicUrl,
 		folders, maxCounts,
+		*volumeUseLevelDb,
 		*serverIp+":"+strconv.Itoa(*masterPort), *volumePulse, *serverDataCenter, *serverRack,
 		serverWhiteList, *volumeFixJpgOrientation,
 	)