Collect the reason why we decided to flush a series (#761)

pkg/ingester/ingester_flush.go

@@ -58,6 +58,16 @@ func (i *Ingester) sweepUsers(immediate bool) {
 	}
 }
 
+type flushReason int
+
+const (
+	noFlush = iota
+	reasonImmediate
+	reasonMultipleChunksInSeries
+	reasonAged
+	reasonIdle
+)
+
 // sweepSeries schedules a series for flushing based on a set of criteria
 //
 // NB we don't close the head chunk here, as the series could wait in the queue
@@ -70,39 +80,42 @@ func (i *Ingester) sweepSeries(userID string, fp model.Fingerprint, series *memo
 	firstTime := series.firstTime()
 	flush := i.shouldFlushSeries(series, immediate)
 
-	if flush {
+	if flush != noFlush {
 		flushQueueIndex := int(uint64(fp) % uint64(i.cfg.ConcurrentFlushes))
-		util.Event().Log("msg", "add to flush queue", "userID", userID, "numChunks", len(series.chunkDescs), "firstTime", firstTime, "fp", fp, "series", series.metric)
+		util.Event().Log("msg", "add to flush queue", "userID", userID, "reason", flush, "firstTime", firstTime, "fp", fp, "series", series.metric)
 		i.flushQueues[flushQueueIndex].Enqueue(&flushOp{firstTime, userID, fp, immediate})
 	}
 }
 
-func (i *Ingester) shouldFlushSeries(series *memorySeries, immediate bool) bool {
+func (i *Ingester) shouldFlushSeries(series *memorySeries, immediate bool) flushReason {
+	if immediate {
+		return reasonImmediate
+	}
 	// Series should be scheduled for flushing if they have more than one chunk
-	if immediate || len(series.chunkDescs) > 1 {
-		return true
+	if len(series.chunkDescs) > 1 {
+		return reasonMultipleChunksInSeries
 	}
 
 	// Or if the only existing chunk need flushing
 	if len(series.chunkDescs) > 0 {
 		return i.shouldFlushChunk(series.chunkDescs[0])
 	}
 
-	return false
+	return noFlush
 }
 
-func (i *Ingester) shouldFlushChunk(c *desc) bool {
+func (i *Ingester) shouldFlushChunk(c *desc) flushReason {
 	// Chunks should be flushed if they span longer than MaxChunkAge
 	if c.LastTime.Sub(c.FirstTime) > i.cfg.MaxChunkAge {
-		return true
+		return reasonAged
 	}
 
 	// Chunk should be flushed if their last update is older then MaxChunkIdle
 	if model.Now().Sub(c.LastUpdate) > i.cfg.MaxChunkIdle {
-		return true
+		return reasonIdle
 	}
 
-	return false
+	return noFlush
 }
 
 func (i *Ingester) flushLoop(j int) {
@@ -148,14 +161,15 @@ func (i *Ingester) flushUserSeries(userID string, fp model.Fingerprint, immediat
 	}
 
 	userState.fpLocker.Lock(fp)
-	if !i.shouldFlushSeries(series, immediate) {
+	reason := i.shouldFlushSeries(series, immediate)
+	if reason == noFlush {
 		userState.fpLocker.Unlock(fp)
 		return nil
 	}
 
 	// Assume we're going to flush everything, and maybe don't flush the head chunk if it doesn't need it.
 	chunks := series.chunkDescs
-	if immediate || (len(chunks) > 0 && i.shouldFlushChunk(series.head())) {
+	if immediate || (len(chunks) > 0 && i.shouldFlushChunk(series.head()) != noFlush) {
 		series.closeHead()
 	} else {
 		chunks = chunks[:len(chunks)-1]
@@ -171,7 +185,7 @@ func (i *Ingester) flushUserSeries(userID string, fp model.Fingerprint, immediat
 	ctx, cancel := context.WithTimeout(ctx, i.cfg.FlushOpTimeout)
 	defer cancel() // releases resources if slowOperation completes before timeout elapses
 
-	util.Event().Log("msg", "flush chunks", "userID", userID, "numChunks", len(chunks), "firstTime", chunks[0].FirstTime, "fp", fp, "series", series.metric)
+	util.Event().Log("msg", "flush chunks", "userID", userID, "reason", reason, "numChunks", len(chunks), "firstTime", chunks[0].FirstTime, "fp", fp, "series", series.metric)
 	err := i.flushChunks(ctx, fp, series.metric, chunks)
 	if err != nil {
 		util.Event().Log("msg", "flush error", "userID", userID, "err", err, "fp", fp, "series", series.metric)