add queue_time slice to query_duration_seconds (prometheus#4050)

promql/engine.go

@@ -50,6 +50,7 @@ const (
 type engineMetrics struct {
 	currentQueries       prometheus.Gauge
 	maxConcurrentQueries prometheus.Gauge
+	queryQueueTime       prometheus.Summary
 	queryPrepareTime     prometheus.Summary
 	queryInnerEval       prometheus.Summary
 	queryResultAppend    prometheus.Summary
@@ -177,6 +178,13 @@ func NewEngine(logger log.Logger, reg prometheus.Registerer, maxConcurrent int,
 			Name:      "queries_concurrent_max",
 			Help:      "The max number of concurrent queries.",
 		}),
+		queryQueueTime: prometheus.NewSummary(prometheus.SummaryOpts{
+			Namespace:   namespace,
+			Subsystem:   subsystem,
+			Name:        "query_duration_seconds",
+			Help:        "Query timings",
+			ConstLabels: prometheus.Labels{"slice": "queue_time"},
+		}),
 		queryPrepareTime: prometheus.NewSummary(prometheus.SummaryOpts{
 			Namespace:   namespace,
 			Subsystem:   subsystem,
@@ -308,6 +316,7 @@ func (ng *Engine) exec(ctx context.Context, q *query) (Value, error) {
 	defer ng.gate.Done()
 
 	queueTimer.Stop()
+	ng.metrics.queryQueueTime.Observe(queueTimer.ElapsedTime().Seconds())
 
 	// Cancel when execution is done or an error was raised.
 	defer q.cancel()