Collect latency metrics on Transaction.Commit()

db/event_listener.go

@@ -4,14 +4,22 @@ import "time"
 
 type EventListener interface {
 	OnIO(write bool, duration time.Duration)
+	OnCommit(duration time.Duration)
 }
 
 type SelectiveListener struct {
-	OnIOCb func(write bool, duration time.Duration)
+	OnIOCb     func(write bool, duration time.Duration)
+	OnCommitCb func(duration time.Duration)
 }
 
 func (l *SelectiveListener) OnIO(write bool, duration time.Duration) {
 	if l.OnIOCb != nil {
 		l.OnIOCb(write, duration)
 	}
 }
+
+func (l *SelectiveListener) OnCommit(duration time.Duration) {
+	if l.OnCommitCb != nil {
+		l.OnCommitCb(duration)
+	}
+}

db/pebble/db_test.go

@@ -30,6 +30,8 @@ func (l *eventListener) OnIO(write bool, _ time.Duration) {
 	}
 }
 
+func (l *eventListener) OnCommit(_ time.Duration) {}
+
 func TestTransaction(t *testing.T) {
 	listener := eventListener{}
 	t.Run("new transaction can retrieve existing value", func(t *testing.T) {

db/pebble/transaction.go

@@ -46,6 +46,8 @@ func (t *Transaction) Discard() error {
 
 // Commit : see db.Transaction.Commit
 func (t *Transaction) Commit() error {
+	start := time.Now()
+	defer func() { t.listener.OnCommit(time.Since(start)) }()
 	if t.batch != nil {
 		return utils.RunAndWrapOnError(t.Discard, t.batch.Commit(pebble.Sync))
 	}

node/metrics.go

@@ -39,8 +39,26 @@ func makeDBMetrics() db.EventListener {
 		Name:      "write_latency",
 		Buckets:   latencyBuckets,
 	})
+	commitLatency := prometheus.NewHistogram(prometheus.HistogramOpts{
+		Namespace: "db",
+		Name:      "commit_latency",
+		Buckets: []float64{
+			5000,
+			10000,
+			20000,
+			30000,
+			40000,
+			50000,
+			100000, // 100ms
+			200000,
+			300000,
+			500000,
+			1000000,
+			math.Inf(0),
+		},
+	})
 
-	prometheus.MustRegister(readLatencyHistogram, writeLatencyHistogram)
+	prometheus.MustRegister(readLatencyHistogram, writeLatencyHistogram, commitLatency)
 	return &db.SelectiveListener{
 		OnIOCb: func(write bool, duration time.Duration) {
 			if write {
@@ -49,6 +67,9 @@ func makeDBMetrics() db.EventListener {
 				readLatencyHistogram.Observe(float64(duration.Microseconds()))
 			}
 		},
+		OnCommitCb: func(duration time.Duration) {
+			commitLatency.Observe(float64(duration.Microseconds()))
+		},
 	}
 }