refactor: extract out the write throttler

weed/util/throttler.go

@@ -0,0 +1,34 @@
+package util
+
+import "time"
+
+type WriteThrottler struct {
+	compactionBytePerSecond int64
+	lastSizeCounter         int64
+	lastSizeCheckTime       time.Time
+}
+
+func NewWriteThrottler(bytesPerSecond int64) *WriteThrottler {
+	return &WriteThrottler{
+		compactionBytePerSecond: bytesPerSecond,
+		lastSizeCheckTime:       time.Now(),
+	}
+}
+
+func (wt *WriteThrottler) MaybeSlowdown(delta int64) {
+	if wt.compactionBytePerSecond > 0 {
+		wt.lastSizeCounter += delta
+		now := time.Now()
+		elapsedDuration := now.Sub(wt.lastSizeCheckTime)
+		if elapsedDuration > 100*time.Millisecond {
+			overLimitBytes := wt.lastSizeCounter - wt.compactionBytePerSecond/10
+			if overLimitBytes > 0 {
+				overRatio := float64(overLimitBytes) / float64(wt.compactionBytePerSecond)
+				sleepTime := time.Duration(overRatio*1000) * time.Millisecond
+				// glog.V(0).Infof("currently %d bytes, limit to %d bytes, over by %d bytes, sleeping %v over %.4f", wt.lastSizeCounter, wt.compactionBytePerSecond/10, overLimitBytes, sleepTime, overRatio)
+				time.Sleep(sleepTime)
+			}
+			wt.lastSizeCounter, wt.lastSizeCheckTime = 0, time.Now()
+		}
+	}
+}