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/volume.go

@@ -32,6 +32,7 @@ type VolumeServerOptions struct {
 	dataCenter            *string
 	rack                  *string
 	whiteList             []string
+	useLevelDb            *bool
 	fixJpgOrientation     *bool
 }
 
@@ -48,6 +49,7 @@ func init() {
 	v.maxCpu = cmdVolume.Flag.Int("maxCpu", 0, "maximum number of CPUs. 0 means all available CPUs")
 	v.dataCenter = cmdVolume.Flag.String("dataCenter", "", "current volume server's data center name")
 	v.rack = cmdVolume.Flag.String("rack", "", "current volume server's rack name")
+	v.useLevelDb = cmdVolume.Flag.Bool("leveldb", false, "Change to leveldb mode to save memory with reduced performance of read and write.")
 	v.fixJpgOrientation = cmdVolume.Flag.Bool("images.fix.orientation", true, "Adjust jpg orientation when uploading.")
 }
 
@@ -116,6 +118,7 @@ func runVolume(cmd *Command, args []string) bool {
 	volumeServer := weed_server.NewVolumeServer(volumeMux, publicVolumeMux,
 		*v.ip, *v.port, *v.publicUrl,
 		v.folders, v.folderMaxLimits,
+		*v.useLevelDb,
 		*v.master, *v.pulseSeconds, *v.dataCenter, *v.rack,
 		v.whiteList,
 		*v.fixJpgOrientation,