[release-20.0] fix: App and Dba Pool metrics (#18048)

go/vt/dbconnpool/connection_pool.go

@@ -36,8 +36,16 @@ import (
 // PooledDBConnection objects.
 type ConnectionPool struct {
 	*smartconnpool.ConnPool[*DBConnection]
+
+	name string
 }
 
+// usedNames is for preventing expvar from panicking. Tests
+// create pool objects multiple time. If a name was previously
+// used, expvar initialization is skipped.
+// through non-test code.
+var usedNames = make(map[string]bool)
+
 // NewConnectionPool creates a new ConnectionPool. The name is used
 // to publish stats only.
 func NewConnectionPool(name string, stats *servenv.Exporter, capacity int, idleTimeout time.Duration, maxLifetime time.Duration, dnsResolutionFrequency time.Duration) *ConnectionPool {
@@ -47,7 +55,18 @@ func NewConnectionPool(name string, stats *servenv.Exporter, capacity int, idleT
 		MaxLifetime:     maxLifetime,
 		RefreshInterval: dnsResolutionFrequency,
 	}
-	return &ConnectionPool{ConnPool: smartconnpool.NewPool(&config)}
+	cp := &ConnectionPool{ConnPool: smartconnpool.NewPool(&config), name: name}
+	if name == "" || usedNames[name] {
+		return cp
+	}
+	usedNames[name] = true
+
+	if stats == nil {
+		// This is unnamed exported so it will use the stats functions directly when adding to the expvar.
+		stats = servenv.NewExporter("", "")
+	}
+	cp.ConnPool.RegisterStats(stats, name)
+	return cp
 }
 
 // Open must be called before starting to use the pool.

go/vt/vttablet/endtoend/config_test.go

@@ -279,6 +279,29 @@ func TestQueryTimeout(t *testing.T) {
 	compareIntDiff(t, vend, "Kills/Connections", vstart, 1)
 }
 
+// TestHeartbeatMetric validates the heartbeat metrics exists from the connection pool.
+func TestHeartbeatMetric(t *testing.T) {
+	tcases := []struct {
+		metricName string
+		exp        any
+	}{{
+		metricName: "HeartbeatWriteAppPoolCapacity",
+		exp:        2,
+	}, {
+		metricName: "HeartbeatWriteAllPrivsPoolCapacity",
+		exp:        2,
+	}}
+
+	metrics := framework.DebugVars()
+	for _, tcase := range tcases {
+		t.Run(tcase.metricName, func(t *testing.T) {
+			mValue, exists := metrics[tcase.metricName]
+			require.True(t, exists, "metric %s not found", tcase.metricName)
+			require.EqualValues(t, tcase.exp, mValue, "metric %s value is %d, want %d", tcase.metricName, mValue, tcase.exp)
+		})
+	}
+}
+
 func changeVar(t *testing.T, name, value string) (revert func()) {
 	t.Helper()
 

go/vt/vttablet/endtoend/framework/server.go

@@ -129,6 +129,9 @@ func StartServer(ctx context.Context, connParams, connAppDebugParams mysql.ConnP
 	config.EnableViews = true
 	config.QueryCacheDoorkeeper = false
 	config.SchemaReloadInterval = 5 * time.Second
+	config.ReplicationTracker.Mode = tabletenv.Heartbeat
+	config.ReplicationTracker.HeartbeatOnDemand = 1 * time.Second
+	config.ReplicationTracker.HeartbeatInterval = 1 * time.Second
 	gotBytes, _ := yaml2.Marshal(config)
 	log.Infof("Config:\n%s", gotBytes)
 	return StartCustomServer(ctx, connParams, connAppDebugParams, dbName, config)