fix: App and Dba Pool metrics (#18048)

Signed-off-by: Harshit Gangal <[email protected]>

Author: vitess-bot[bot]

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()