Expose EmptyAcquireWaitTime as prometheus counter

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

Author: gearnode

pg/client_test.go

@@ -222,6 +222,46 @@ func TestNewClient(t *testing.T) {
 			)
 		},
 	)
+
+	t.Run(
+		"exposes expected pgxpool metrics",
+		func(t *testing.T) {
+			reg := prometheus.NewRegistry()
+			_, err := pg.NewClient(
+				pg.WithAddr("localhost:5432"),
+				pg.WithRegisterer(reg),
+			)
+			require.NoError(t, err)
+
+			families, err := reg.Gather()
+			require.NoError(t, err)
+
+			got := make(map[string]struct{}, len(families))
+			for _, fam := range families {
+				got[fam.GetName()] = struct{}{}
+			}
+
+			expected := []string{
+				"pgxpool_acquire_total",
+				"pgxpool_acquire_duration_seconds",
+				"pgxpool_acquired_connections",
+				"pgxpool_canceled_acquire_total",
+				"pgxpool_constructing_connections",
+				"pgxpool_empty_acquire_total",
+				"pgxpool_empty_acquire_wait_time_seconds",
+				"pgxpool_idle_connections",
+				"pgxpool_max_connections",
+				"pgxpool_total_connections",
+				"pgxpool_new_connections_total",
+				"pgxpool_max_lifetime_destroy_total",
+				"pgxpool_max_idle_destroy_total",
+			}
+			for _, name := range expected {
+				_, ok := got[name]
+				assert.Truef(t, ok, "metric %q not exported", name)
+			}
+		},
+	)
 }
 
 // ---------------------------------------------------------------------------

pg/collector.go

@@ -25,18 +25,19 @@ type (
 	collector struct {
 		pool *pgxpool.Pool
 
-		acquireTotal            *prometheus.Desc
-		acquireDurationSeconds  *prometheus.Desc
-		acquiredConnections     *prometheus.Desc
-		canceledAcquireTotal    *prometheus.Desc
-		constructingConnections *prometheus.Desc
-		emptyAcquireTotal       *prometheus.Desc
-		idleConnections         *prometheus.Desc
-		maxConnections          *prometheus.Desc
-		totalConnections        *prometheus.Desc
-		newConnectionsTotal     *prometheus.Desc
-		maxLifetimeDestroyTotal *prometheus.Desc
-		maxIdleDestroyTotal     *prometheus.Desc
+		acquireTotal                *prometheus.Desc
+		acquireDurationSeconds      *prometheus.Desc
+		acquiredConnections         *prometheus.Desc
+		canceledAcquireTotal        *prometheus.Desc
+		constructingConnections     *prometheus.Desc
+		emptyAcquireTotal           *prometheus.Desc
+		emptyAcquireWaitTimeSeconds *prometheus.Desc
+		idleConnections             *prometheus.Desc
+		maxConnections              *prometheus.Desc
+		totalConnections            *prometheus.Desc
+		newConnectionsTotal         *prometheus.Desc
+		maxLifetimeDestroyTotal     *prometheus.Desc
+		maxIdleDestroyTotal         *prometheus.Desc
 	}
 
 	statWrapper struct {
@@ -84,6 +85,12 @@ func newCollector(pool *pgxpool.Pool, labels map[string]string) *collector {
 			nil,
 			labels,
 		),
+		emptyAcquireWaitTimeSeconds: prometheus.NewDesc(
+			"pgxpool_empty_acquire_wait_time_seconds",
+			"Cumulative time in seconds waited for successful acquires from the pool that had to wait for a resource to be released or constructed because the pool was empty. Dividing by pgxpool_empty_acquire_total yields the mean slow-path acquire latency, which isolates connection construction and contention from the fast-path (idle conn handover).",
+			nil,
+			labels,
+		),
 		idleConnections: prometheus.NewDesc(
 			"pgxpool_idle_connections",
 			"Number of currently idle connections in the pool.",
@@ -160,6 +167,11 @@ func (c *collector) Collect(metrics chan<- prometheus.Metric) {
 		prometheus.CounterValue,
 		stats.emptyAcquireCount(),
 	)
+	metrics <- prometheus.MustNewConstMetric(
+		c.emptyAcquireWaitTimeSeconds,
+		prometheus.CounterValue,
+		stats.emptyAcquireWaitTime(),
+	)
 	metrics <- prometheus.MustNewConstMetric(
 		c.idleConnections,
 		prometheus.GaugeValue,
@@ -210,6 +222,9 @@ func (w *statWrapper) constructingConns() float64 {
 func (w *statWrapper) emptyAcquireCount() float64 {
 	return float64(w.stats.EmptyAcquireCount())
 }
+func (w *statWrapper) emptyAcquireWaitTime() float64 {
+	return w.stats.EmptyAcquireWaitTime().Seconds()
+}
 func (w *statWrapper) idleConns() float64 {
 	return float64(w.stats.IdleConns())
 }