volume: avoid sharing volume dat file handle

possibly help on https://github.com/chrislusf/seaweedfs/issues/1184

weed/storage/volume_vacuum.go

@@ -72,7 +72,7 @@ func (v *Volume) Compact2(preallocate int64) error {
 	v.lastCompactIndexOffset = v.IndexFileSize()
 	v.lastCompactRevision = v.SuperBlock.CompactionRevision
 	glog.V(3).Infof("creating copies for volume %d ...", v.Id)
-	return v.copyDataBasedOnIndexFile(filePath+".cpd", filePath+".cpx", preallocate)
+	return copyDataBasedOnIndexFile(filePath+".dat", filePath+".idx", filePath+".cpd", filePath+".cpx", v.SuperBlock, v.Version(), preallocate)
 }
 
 func (v *Volume) CommitCompact() error {
@@ -353,26 +353,31 @@ func (v *Volume) copyDataAndGenerateIndexFile(dstName, idxName string, prealloca
 	return
 }
 
-func (v *Volume) copyDataBasedOnIndexFile(dstName, idxName string, preallocate int64) (err error) {
+func copyDataBasedOnIndexFile(srcDatName, srcIdxName, dstDatName, datIdxName string, sb super_block.SuperBlock, version needle.Version, preallocate int64) (err error) {
 	var (
-		dstDatBackend backend.BackendStorageFile
+		srcDatBackend, dstDatBackend backend.BackendStorageFile
+		dataFile *os.File
 	)
-	if dstDatBackend, err = createVolumeFile(dstName, preallocate, 0); err != nil {
+	if dstDatBackend, err = createVolumeFile(dstDatName, preallocate, 0); err != nil {
 		return
 	}
 	defer dstDatBackend.Close()
 
 	oldNm := needle_map.NewMemDb()
 	newNm := needle_map.NewMemDb()
-	if err = oldNm.LoadFromIdx(v.FileName()+".idx"); err != nil {
+	if err = oldNm.LoadFromIdx(srcIdxName); err != nil {
 		return
 	}
+	if dataFile, err = os.Open(srcDatName); err != nil {
+		return err
+	}
+	srcDatBackend = backend.NewDiskFile(dataFile)
 
 	now := uint64(time.Now().Unix())
 
-	v.SuperBlock.CompactionRevision++
-	dstDatBackend.WriteAt(v.SuperBlock.Bytes(), 0)
-	newOffset := int64(v.SuperBlock.BlockSize())
+	sb.CompactionRevision++
+	dstDatBackend.WriteAt(sb.Bytes(), 0)
+	newOffset := int64(sb.BlockSize())
 
 	oldNm.AscendingVisit(func(value needle_map.NeedleValue) error {
 
@@ -383,28 +388,28 @@ func (v *Volume) copyDataBasedOnIndexFile(dstName, idxName string, preallocate i
 		}
 
 		n := new(needle.Needle)
-		err := n.ReadData(v.DataBackend, offset.ToAcutalOffset(), size, v.Version())
+		err := n.ReadData(srcDatBackend, offset.ToAcutalOffset(), size, version)
 		if err != nil {
 			return nil
 		}
 
-		if n.HasTtl() && now >= n.LastModified+uint64(v.Ttl.Minutes()*60) {
+		if n.HasTtl() && now >= n.LastModified+uint64(sb.Ttl.Minutes()*60) {
 			return nil
 		}
 
 		if err = newNm.Set(n.Id, ToOffset(newOffset), n.Size); err != nil {
 			return fmt.Errorf("cannot put needle: %s", err)
 		}
-		if _, _, _, err = n.Append(dstDatBackend, v.Version()); err != nil {
+		if _, _, _, err = n.Append(dstDatBackend, sb.Version); err != nil {
 			return fmt.Errorf("cannot append needle: %s", err)
 		}
-		newOffset += n.DiskSize(v.Version())
+		newOffset += n.DiskSize(version)
 		glog.V(3).Infoln("saving key", n.Id, "volume offset", offset, "=>", newOffset, "data_size", n.Size)
 
 		return nil
 	})
 
-	newNm.SaveToIdx(idxName)
+	newNm.SaveToIdx(datIdxName)
 
 	return
 }