diff --git a/weed/filer/reader_at.go b/weed/filer/reader_at.go
index a38a0bfd5..8ee627a21 100644
--- a/weed/filer/reader_at.go
+++ b/weed/filer/reader_at.go
@@ -21,6 +21,7 @@ type ChunkReadAt struct {
 	fileSize      int64
 	readerCache   *ReaderCache
 	readerPattern *ReaderPattern
+	lastChunkFid  string
 }
 
 var _ = io.ReaderAt(&ChunkReadAt{})
@@ -85,7 +86,7 @@ func NewChunkReaderAtFromClient(lookupFn wdclient.LookupFileIdFunctionType, chun
 	return &ChunkReadAt{
 		chunkViews:    chunkViews,
 		fileSize:      fileSize,
-		readerCache:   newReaderCache(5, chunkCache, lookupFn),
+		readerCache:   newReaderCache(32, chunkCache, lookupFn),
 		readerPattern: NewReaderPattern(),
 	}
 }
@@ -167,12 +168,12 @@ func (c *ChunkReadAt) readChunkSliceAt(buffer []byte, chunkView *ChunkView, next
 	}
 
 	n, err = c.readerCache.ReadChunkAt(buffer, chunkView.FileId, chunkView.CipherKey, chunkView.IsGzipped, int64(offset), int(chunkView.ChunkSize), chunkView.LogicOffset == 0)
-	for i, nextChunk := range nextChunkViews {
-		if i < 2 {
-			c.readerCache.MaybeCache(nextChunk.FileId, nextChunk.CipherKey, nextChunk.IsGzipped, int(nextChunk.ChunkSize))
-		} else {
-			break
+	if c.lastChunkFid != "" && c.lastChunkFid != chunkView.FileId {
+		if chunkView.Offset == 0 { // start of a new chunk
+			c.readerCache.UnCache(c.lastChunkFid)
+			c.readerCache.MaybeCache(nextChunkViews)
 		}
 	}
+	c.lastChunkFid = chunkView.FileId
 	return
 }
diff --git a/weed/filer/reader_cache.go b/weed/filer/reader_cache.go
index 1a0dc6a31..4f2c52303 100644
--- a/weed/filer/reader_cache.go
+++ b/weed/filer/reader_cache.go
@@ -40,41 +40,33 @@ func newReaderCache(limit int, chunkCache chunk_cache.ChunkCache, lookupFileIdFn
 	}
 }
 
-func (rc *ReaderCache) MaybeCache(fileId string, cipherKey []byte, isGzipped bool, chunkSize int) {
-	rc.Lock()
-	defer rc.Unlock()
-	if _, found := rc.downloaders[fileId]; found {
-		return
-	}
+func (rc *ReaderCache) MaybeCache(chunkViews []*ChunkView) {
 	if rc.lookupFileIdFn == nil {
 		return
 	}
 
-	// if too many, delete one of them?
-	if len(rc.downloaders) >= rc.limit {
-		oldestFid, oldestTime := "", time.Now()
-		for fid, downloader := range rc.downloaders {
-			if !downloader.completedTime.IsZero() {
-				if downloader.completedTime.Before(oldestTime) {
-					oldestFid, oldestTime = fid, downloader.completedTime
-				}
-			}
+	rc.Lock()
+	defer rc.Unlock()
+
+	for _, chunkView := range chunkViews {
+		if _, found := rc.downloaders[chunkView.FileId]; found {
+			continue
 		}
-		if oldestFid != "" {
-			oldDownloader := rc.downloaders[oldestFid]
-			delete(rc.downloaders, oldestFid)
-			oldDownloader.destroy()
-		} else {
+
+		if len(rc.downloaders) >= rc.limit {
 			// if still no slots, return
 			return
 		}
-	}
 
-	cacher := newSingleChunkCacher(rc, fileId, cipherKey, isGzipped, chunkSize, false)
-	cacher.wg.Add(1)
-	go cacher.startCaching()
-	cacher.wg.Wait()
-	rc.downloaders[fileId] = cacher
+		// glog.V(4).Infof("prefetch %s offset %d", chunkView.FileId, chunkView.LogicOffset)
+		// cache this chunk if not yet
+		cacher := newSingleChunkCacher(rc, chunkView.FileId, chunkView.CipherKey, chunkView.IsGzipped, int(chunkView.ChunkSize), false)
+		cacher.wg.Add(1)
+		go cacher.startCaching()
+		cacher.wg.Wait()
+		rc.downloaders[chunkView.FileId] = cacher
+
+	}
 
 	return
 }
@@ -108,6 +100,8 @@ func (rc *ReaderCache) ReadChunkAt(buffer []byte, fileId string, cipherKey []byt
 		}
 	}
 
+	// glog.V(4).Infof("cache1 %s", fileId)
+
 	cacher := newSingleChunkCacher(rc, fileId, cipherKey, isGzipped, chunkSize, shouldCache)
 	cacher.wg.Add(1)
 	go cacher.startCaching()
@@ -117,6 +111,16 @@ func (rc *ReaderCache) ReadChunkAt(buffer []byte, fileId string, cipherKey []byt
 	return cacher.readChunkAt(buffer, offset)
 }
 
+func (rc *ReaderCache) UnCache(fileId string) {
+	rc.Lock()
+	defer rc.Unlock()
+	// glog.V(4).Infof("uncache %s", fileId)
+	if downloader, found := rc.downloaders[fileId]; found {
+		downloader.destroy()
+		delete(rc.downloaders, fileId)
+	}
+}
+
 func (rc *ReaderCache) destroy() {
 	rc.Lock()
 	defer rc.Unlock()