make chunkRefMap free threshold relative to size

Signed-off-by: Mauro Stettler <mauro.stettler@gmail.com>

tsdb/chunks/chunk_write_queue.go

@@ -24,7 +24,6 @@ import (
 )
 
 const (
-	chunkRefMapFreeThreshold   = 10
 	chunkRefMapMinFreeInterval = 10 * time.Minute
 )
 
@@ -44,10 +43,11 @@ type chunkWriteJob struct {
 type chunkWriteQueue struct {
 	jobs chan chunkWriteJob
 
-	chunkRefMapMtx      sync.RWMutex
-	chunkRefMap         map[ChunkDiskMapperRef]chunkenc.Chunk
-	chunkRefMapPeak     int
-	chunkRefMapLastFree time.Time
+	chunkRefMapMtx       sync.RWMutex
+	chunkRefMap          map[ChunkDiskMapperRef]chunkenc.Chunk
+	chunkRefMapPeak      int
+	chunkRefMapFreeThres int
+	chunkRefMapLastFree  time.Time
 
 	isRunningMtx sync.Mutex // Protects the isRunning property.
 	isRunning    bool       // Used to prevent that new jobs get added to the queue when the chan is already closed.
@@ -76,10 +76,11 @@ func newChunkWriteQueue(reg prometheus.Registerer, size int, writeChunk writeChu
 	)
 
 	q := &chunkWriteQueue{
-		jobs:                make(chan chunkWriteJob, size),
-		chunkRefMap:         make(map[ChunkDiskMapperRef]chunkenc.Chunk),
-		chunkRefMapLastFree: time.Now(),
-		writeChunk:          writeChunk,
+		jobs:                 make(chan chunkWriteJob, size),
+		chunkRefMap:          make(map[ChunkDiskMapperRef]chunkenc.Chunk),
+		chunkRefMapFreeThres: size / 10,
+		chunkRefMapLastFree:  time.Now(),
+		writeChunk:           writeChunk,
 
 		adds:      counters.WithLabelValues("add"),
 		gets:      counters.WithLabelValues("get"),
@@ -122,7 +123,7 @@ func (c *chunkWriteQueue) processJob(job chunkWriteJob) {
 
 	c.completed.Inc()
 
-	if len(c.chunkRefMap) == 0 && c.chunkRefMapPeak > chunkRefMapFreeThreshold && time.Since(c.chunkRefMapLastFree) > chunkRefMapMinFreeInterval {
+	if len(c.chunkRefMap) == 0 && c.chunkRefMapPeak > c.chunkRefMapFreeThres && time.Since(c.chunkRefMapLastFree) > chunkRefMapMinFreeInterval {
 		// Re-initialize the chunk ref map to half of the peak size that was in use since the last re-init event.
 		// By setting it to half of the peak we try to minimize the number of allocations required for a "normal" usage
 		// while ensuring that if its usage has decreased we shrink it over time.