server: add token usage gauge for tidb (#22511)

Signed-off-by: iosmanthus <myosmanthustree@gmail.com>

metrics/metrics.go

@@ -175,4 +175,6 @@ func RegisterMetrics() {
 	prometheus.MustRegister(GOGC)
 	prometheus.MustRegister(ConnIdleDurationHistogram)
 	prometheus.MustRegister(ServerInfo)
+	prometheus.MustRegister(TokenGauge)
+	prometheus.MustRegister(TokenLimitGauge)
 }

metrics/server.go

@@ -203,6 +203,24 @@ var (
 			Name:      "info",
 			Help:      "Indicate the tidb server info, and the value is the start timestamp (s).",
 		}, []string{LblVersion, LblHash})
+
+	TokenGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "tidb",
+			Subsystem: "server",
+			Name:      "tokens",
+			Help:      "The number of concurrent executing session",
+		},
+	)
+
+	TokenLimitGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "tidb",
+			Subsystem: "server",
+			Name:      "token_limit",
+			Help:      "The maximum number of concurrent executing session",
+		},
+	)
 )
 
 // ExecuteErrorToLabel converts an execute error to label.

server/server.go

@@ -141,6 +141,7 @@ func (s *Server) ConnectionCount() int {
 func (s *Server) getToken() *Token {
 	start := time.Now()
 	tok := s.concurrentLimiter.Get()
+	metrics.TokenGauge.Inc()
 	// Note that data smaller than one microsecond is ignored, because that case can be viewed as non-block.
 	metrics.GetTokenDurationHistogram.Observe(float64(time.Since(start).Nanoseconds() / 1e3))
 	return tok
@@ -148,6 +149,7 @@ func (s *Server) getToken() *Token {
 
 func (s *Server) releaseToken(token *Token) {
 	s.concurrentLimiter.Put(token)
+	metrics.TokenGauge.Dec()
 }
 
 // SetDomain use to set the server domain.
@@ -304,9 +306,15 @@ func setTxnScope() {
 	variable.SetSysVar("txn_scope", config.GetGlobalConfig().TxnScope)
 }
 
+// Export config-related metrics
+func (s *Server) reportConfig() {
+	metrics.TokenLimitGauge.Set(float64(s.cfg.TokenLimit))
+}
+
 // Run runs the server.
 func (s *Server) Run() error {
 	metrics.ServerEventCounter.WithLabelValues(metrics.EventStart).Inc()
+	s.reportConfig()
 
 	// Start HTTP API to report tidb info such as TPS.
 	if s.cfg.Status.ReportStatus {