add btree for volume index

weed/storage/needle/needle_value.go

@@ -0,0 +1,28 @@
+package needle
+
+import (
+	"strconv"
+
+	"github.com/google/btree"
+)
+
+const (
+	batch = 100000
+)
+
+type NeedleValue struct {
+	Key    Key
+	Offset uint32 `comment:"Volume offset"` //since aligned to 8 bytes, range is 4G*8=32G
+	Size   uint32 `comment:"Size of the data portion"`
+}
+
+func (this NeedleValue) Less(than btree.Item) bool {
+	that := than.(NeedleValue)
+	return this.Key < that.Key
+}
+
+type Key uint64
+
+func (k Key) String() string {
+	return strconv.FormatUint(uint64(k), 10)
+}