mount: adds read prefetching

weed/filer/reader_at.go

@@ -19,7 +19,10 @@ type ChunkReadAt struct {
 	readerLock   sync.Mutex
 	fileSize     int64
 
-	chunkCache chunk_cache.ChunkCache
+	lastChunkFileId string
+	lastChunkData   []byte
+	isPrefetching   bool
+	chunkCache      chunk_cache.ChunkCache
 }
 
 // var _ = io.ReaderAt(&ChunkReadAt{})
@@ -76,10 +79,16 @@ func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
 
 	var buffer []byte
 	startOffset, remaining := offset, int64(len(p))
+	var nextChunkView *ChunkView
 	for i, chunk := range c.chunkViews {
 		if remaining <= 0 {
 			break
 		}
+		if i+1 < len(c.chunkViews) {
+			nextChunkView = c.chunkViews[i+1]
+		} else {
+			nextChunkView = nil
+		}
 		if startOffset < chunk.LogicOffset {
 			gap := int(chunk.LogicOffset - startOffset)
 			glog.V(4).Infof("zero [%d,%d)", startOffset, startOffset+int64(gap))
@@ -95,7 +104,7 @@ func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
 			continue
 		}
 		glog.V(4).Infof("read [%d,%d), %d/%d chunk %s [%d,%d)", chunkStart, chunkStop, i, len(c.chunkViews), chunk.FileId, chunk.LogicOffset-chunk.Offset, chunk.LogicOffset-chunk.Offset+int64(chunk.Size))
-		buffer, err = c.readFromWholeChunkData(chunk)
+		buffer, err = c.readFromWholeChunkData(chunk, nextChunkView)
 		if err != nil {
 			glog.Errorf("fetching chunk %+v: %v\n", chunk, err)
 			return
@@ -123,27 +132,45 @@ func (c *ChunkReadAt) doReadAt(p []byte, offset int64) (n int, err error) {
 
 }
 
-func (c *ChunkReadAt) readFromWholeChunkData(chunkView *ChunkView) (chunkData []byte, err error) {
+func (c *ChunkReadAt) readFromWholeChunkData(chunkView *ChunkView, nextChunkView *ChunkView) (chunkData []byte, err error) {
 
 	glog.V(4).Infof("readFromWholeChunkData %s offset %d [%d,%d) size at least %d", chunkView.FileId, chunkView.Offset, chunkView.LogicOffset, chunkView.LogicOffset+int64(chunkView.Size), chunkView.ChunkSize)
 
+	if c.lastChunkFileId == chunkView.FileId {
+		return c.lastChunkData, nil
+	}
+
 	chunkData = c.chunkCache.GetChunk(chunkView.FileId, chunkView.ChunkSize)
 	if chunkData != nil {
 		glog.V(4).Infof("cache hit %s [%d,%d)", chunkView.FileId, chunkView.LogicOffset-chunkView.Offset, chunkView.LogicOffset-chunkView.Offset+int64(len(chunkData)))
 	} else {
 		glog.V(4).Infof("doFetchFullChunkData %s", chunkView.FileId)
-		chunkData, err = c.doFetchFullChunkData(chunkView.FileId, chunkView.CipherKey, chunkView.IsGzipped)
+		chunkData, err = c.doFetchFullChunkData(chunkView)
 		if err != nil {
 			return
 		}
 		c.chunkCache.SetChunk(chunkView.FileId, chunkData)
 	}
 
+	c.lastChunkData = chunkData
+	c.lastChunkFileId = chunkView.FileId
+	if nextChunkView != nil && !c.isPrefetching {
+		c.isPrefetching = true
+		go func() {
+			if chunkData, err := c.doFetchFullChunkData(nextChunkView); err == nil {
+				c.chunkCache.SetChunk(nextChunkView.FileId, chunkData)
+			}
+			c.isPrefetching = false
+		}()
+	}
+
+
 	return
 }
 
-func (c *ChunkReadAt) doFetchFullChunkData(fileId string, cipherKey []byte, isGzipped bool) ([]byte, error) {
+func (c *ChunkReadAt) doFetchFullChunkData(chunkView *ChunkView) ([]byte, error) {
 
-	return fetchChunk(c.lookupFileId, fileId, cipherKey, isGzipped)
+	data, err := fetchChunk(c.lookupFileId, chunkView.FileId, chunkView.CipherKey, chunkView.IsGzipped)
+	return data, err
 
 }