write to disk during random writes, limiting total disk spaces used

weed/mount/page_writer_pattern.go

@@ -0,0 +1,44 @@
+package mount
+
+type WriterPattern struct {
+	isStreaming     bool
+	lastWriteOffset int64
+	chunkSize       int64
+}
+
+// For streaming write: only cache the first chunk
+// For random write: fall back to temp file approach
+// writes can only change from streaming mode to non-streaming mode
+
+func NewWriterPattern(chunkSize int64) *WriterPattern {
+	return &WriterPattern{
+		isStreaming:     true,
+		lastWriteOffset: -1,
+		chunkSize:       chunkSize,
+	}
+}
+
+func (rp *WriterPattern) MonitorWriteAt(offset int64, size int) {
+	if rp.lastWriteOffset > offset {
+		rp.isStreaming = false
+	}
+	if rp.lastWriteOffset == -1 {
+		if offset != 0 {
+			rp.isStreaming = false
+		}
+	}
+	rp.lastWriteOffset = offset
+}
+
+func (rp *WriterPattern) IsStreamingMode() bool {
+	return rp.isStreaming
+}
+
+func (rp *WriterPattern) IsRandomMode() bool {
+	return !rp.isStreaming
+}
+
+func (rp *WriterPattern) Reset() {
+	rp.isStreaming = true
+	rp.lastWriteOffset = -1
+}