mount: improve read performance on random reads

weed/filer/reader_pattern.go

@@ -0,0 +1,31 @@
+package filer
+
+type ReaderPattern struct {
+	isStreaming    bool
+	lastReadOffset int64
+}
+
+// For streaming read: only cache the first chunk
+// For random read: only fetch the requested range, instead of the whole chunk
+
+func NewReaderPattern() *ReaderPattern {
+	return &ReaderPattern{
+		isStreaming:    true,
+		lastReadOffset: 0,
+	}
+}
+
+func (rp *ReaderPattern) MonitorReadAt(offset int64, size int) {
+	if rp.lastReadOffset > offset {
+		rp.isStreaming = false
+	}
+	rp.lastReadOffset = offset
+}
+
+func (rp *ReaderPattern) IsStreamingMode() bool {
+	return rp.isStreaming
+}
+
+func (rp *ReaderPattern) IsRandomMode() bool {
+	return !rp.isStreaming
+}