use NeedleValue directly instead of additional pointer, to reduce memory

usage

weed-fs/src/pkg/storage/needle_map.go

@@ -13,13 +13,13 @@ type NeedleValue struct {
 
 type NeedleMap struct {
 	indexFile *os.File
-	m         map[uint64]*NeedleValue //mapping needle key(uint64) to NeedleValue
+	m         map[uint64]NeedleValue //mapping needle key(uint64) to NeedleValue
 	bytes     []byte
 }
 
 func NewNeedleMap(file *os.File) *NeedleMap {
 	nm := &NeedleMap{
-		m:         make(map[uint64]*NeedleValue),
+		m:         make(map[uint64]NeedleValue),
 		bytes:     make([]byte, 16),
 		indexFile: file,
 	}
@@ -44,7 +44,7 @@ func LoadNeedleMap(file *os.File) *NeedleMap {
 			offset := util.BytesToUint32(bytes[i+8 : i+12])
 			size := util.BytesToUint32(bytes[i+12 : i+16])
 			if offset>0 {
-   			nm.m[key] = &NeedleValue{util.Offset: offset, Size: size}
+   			nm.m[key] = NeedleValue{util.Offset: offset, Size: size}
    	  }else{
         delete(nm.m, key)
    	  }
@@ -56,13 +56,13 @@ func LoadNeedleMap(file *os.File) *NeedleMap {
 }     
 
 func (nm *NeedleMap) Put(key uint64, offset uint32, size uint32) (int, error) {
-	nm.m[key] = &NeedleValue{Offset: offset, Size: size}
+	nm.m[key] = NeedleValue{Offset: offset, Size: size}
 	util.Uint64toBytes(nm.bytes[0:8], key)
 	util.Uint32toBytes(nm.bytes[8:12], offset)
 	util.Uint32toBytes(nm.bytes[12:16], size)
 	return nm.indexFile.Write(nm.bytes)
 }
-func (nm *NeedleMap) Get(key uint64) (element *NeedleValue, ok bool) {
+func (nm *NeedleMap) Get(key uint64) (element NeedleValue, ok bool) {
 	element, ok = nm.m[key]
 	return
 }
@@ -76,3 +76,6 @@ func (nm *NeedleMap) Delete(key uint64) {
 func (nm *NeedleMap) Close() {
 	nm.indexFile.Close()
 }
+func (nm *NeedleMap) Length() int{
+  return len(nm.m)
+}