Change Mutex to RWMutex

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

plugins/outputs/clickhouse/clickhouse.go

@@ -48,7 +48,7 @@ type ClickHouse struct {
 	db            *sql.DB
 	Log           telegraf.Logger
 	metricQueue   []telegraf.Metric
-	metricLock    sync.Mutex
+	metricLock    sync.RWMutex
 	metricTrigger chan struct{}
 }
 
@@ -441,12 +441,17 @@ func (ch *ClickHouse) WriteSingleTable(metrics []telegraf.Metric) error {
 }
 
 func (ch *ClickHouse) Write(metrics []telegraf.Metric) error {
-	ch.metricLock.Lock()
-	if len(ch.metricQueue) >= ch.QueueMaxSize {
-		ch.Log.Errorf("Metrics queue is full (%d/%d), dropping metrics", len(ch.metricQueue), ch.QueueMaxSize)
-	} else {
-		ch.metricQueue = append(ch.metricQueue, metrics...)
+	ch.metricLock.RLock()
+	metricsLength := len(ch.metricQueue)
+	ch.metricLock.RUnlock()
+
+	if metricsLength >= ch.QueueMaxSize {
+		ch.Log.Errorf("Metrics queue is full (%d/%d), dropping metrics", metricsLength, ch.QueueMaxSize)
+		return nil
 	}
+
+	ch.metricLock.Lock()
+	ch.metricQueue = append(ch.metricQueue, metrics...)
 	ch.metricLock.Unlock()
 
 	select {
@@ -464,12 +469,15 @@ func (ch *ClickHouse) backgroundWriter(delay time.Duration) {
 	for {
 		select {
 		case <-timer.C:
-			ch.metricLock.Lock()
+			ch.metricLock.RLock()
 			metrics := ch.metricQueue
-			ch.metricQueue = nil
-			ch.metricLock.Unlock()
+			ch.metricLock.RUnlock()
 
 			if len(metrics) > 0 {
+				ch.metricLock.Lock()
+				ch.metricQueue = make([]telegraf.Metric, 0, ch.QueueInitialSize)
+				ch.metricLock.Unlock()
+
 				if ch.TableMode == "single" {
 					err := ch.WriteSingleTable(metrics)
 					if err != nil {
@@ -486,9 +494,9 @@ func (ch *ClickHouse) backgroundWriter(delay time.Duration) {
 			timer.Reset(delay)
 
 		case <-ch.metricTrigger:
-			ch.metricLock.Lock()
+			ch.metricLock.RLock()
 			metricsLength := len(ch.metricQueue)
-			ch.metricLock.Unlock()
+			ch.metricLock.RUnlock()
 
 			if metricsLength < ch.QueueFlushSize {
 				if !timer.Stop() {

plugins/outputs/clickhouse/sample.conf

@@ -31,11 +31,11 @@
   ## Queue resizes automatically if the queue becomes too large.
   # queue_initial_size = 100000
 
-  ## Maximum queue size, 0 means unlimited
+  ## Maximum queue size, "0" means unlimited
   ## If the queue reaches this size, new writes will be dropped until it drains.
   # queue_max_size = 0
 
-  ## Queue flush size, 0 means unlimited
+  ## Queue flush size, "0" means unlimited
   ## The flush interval will not be reset if the queue is larger than this.
   # queue_flush_size = 0