Repository: nats-io/nats-server (go)

Issue:
Add SlowConsumersStats to stats
### Proposed change

We added `SlowConsumersStats` to varz but a lot of our tooling such as `nats server report` and `nats server watch` are based on statz from `$SYS.REQ.SERVER.PING`.

Lets add `SlowConsumersStats` here also

### Use case

Improved tooling

### Contribution

_No response_

Pull request description:
(2.11) [ADDED] Monitoring: SlowConsumersStats in PING/STATSZ messages
(also fixed a flapper)

Resolves #5877

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>


Patch:
diff --git a/server/events.go b/server/events.go
index 82334dfd..466881e2 100644
--- a/server/events.go
+++ b/server/events.go
@@ -329,21 +329,22 @@ type ClientInfo struct {
 
 // ServerStats hold various statistics that we will periodically send out.
 type ServerStats struct {
-	Start            time.Time      `json:"start"`
-	Mem              int64          `json:"mem"`
-	Cores            int            `json:"cores"`
-	CPU              float64        `json:"cpu"`
-	Connections      int            `json:"connections"`
-	TotalConnections uint64         `json:"total_connections"`
-	ActiveAccounts   int            `json:"active_accounts"`
-	NumSubs          uint32         `json:"subscriptions"`
-	Sent             DataStats      `json:"sent"`
-	Received         DataStats      `json:"received"`
-	SlowConsumers    int64          `json:"slow_consumers"`
-	Routes           []*RouteStat   `json:"routes,omitempty"`
-	Gateways         []*GatewayStat `json:"gateways,omitempty"`
-	ActiveServers    int            `json:"active_servers,omitempty"`
-	JetStream        *JetStreamVarz `json:"jetstream,omitempty"`
+	Start              time.Time           `json:"start"`
+	Mem                int64               `json:"mem"`
+	Cores              int                 `json:"cores"`
+	CPU                float64             `json:"cpu"`
+	Connections        int                 `json:"connections"`
+	TotalConnections   uint64              `json:"total_connections"`
+	ActiveAccounts     int                 `json:"active_accounts"`
+	NumSubs            uint32              `json:"subscriptions"`
+	Sent               DataStats           `json:"sent"`
+	Received           DataStats           `json:"received"`
+	SlowConsumers      int64               `json:"slow_consumers"`
+	SlowConsumersStats *SlowConsumersStats `json:"slow_consumer_stats,omitempty"`
+	Routes             []*RouteStat        `json:"routes,omitempty"`
+	Gateways           []*GatewayStat      `json:"gateways,omitempty"`
+	ActiveServers      int                 `json:"active_servers,omitempty"`
+	JetStream          *JetStreamVarz      `json:"jetstream,omitempty"`
 }
 
 // RouteStat holds route statistics.
@@ -880,6 +881,16 @@ func (s *Server) sendStatsz(subj string) {
 	m.Stats.Sent.Msgs = atomic.LoadInt64(&s.outMsgs)
 	m.Stats.Sent.Bytes = atomic.LoadInt64(&s.outBytes)
 	m.Stats.SlowConsumers = atomic.LoadInt64(&s.slowConsumers)
+	// Evaluate the slow consumer stats, but set it only if one of the value is not 0.
+	scs := &SlowConsumersStats{
+		Clients:  s.NumSlowConsumersClients(),
+		Routes:   s.NumSlowConsumersRoutes(),
+		Gateways: s.NumSlowConsumersGateways(),
+		Leafs:    s.NumSlowConsumersLeafs(),
+	}
+	if scs.Clients != 0 || scs.Routes != 0 || scs.Gateways != 0 || scs.Leafs != 0 {
+		m.Stats.SlowConsumersStats = scs
+	}
 	m.Stats.NumSubs = s.numSubscriptions()
 	// Routes
 	s.forEachRoute(func(r *client) {


Test patch:
diff --git a/server/events_test.go b/server/events_test.go
index 0ffcfe22..b3c7a1ef 100644
--- a/server/events_test.go
+++ b/server/events_test.go
@@ -3687,6 +3687,7 @@ func TestServerEventsStatsZJetStreamApiLevel(t *testing.T) {
 	url := fmt.Sprintf("nats://%s:%d", opts.Host, opts.Port)
 	ncs, err := nats.Connect(url, createUserCreds(t, s, akp))
 	require_NoError(t, err)
+	defer ncs.Close()
 
 	msg, err := ncs.Request("$SYS.REQ.SERVER.PING.STATSZ", nil, time.Second)
 	require_NoError(t, err)
@@ -3697,3 +3698,63 @@ func TestServerEventsStatsZJetStreamApiLevel(t *testing.T) {
 
 	require_Equal(t, stats.Stats.JetStream.Stats.API.Level, JSApiLevel)
 }
+
+func TestServerEventsPingStatsSlowConsumersStats(t *testing.T) {
+	s, _ := runTrustedServer(t)
+	defer s.Shutdown()
+
+	acc, akp := createAccount(s)
+	s.setSystemAccount(acc)
+	ncs, err := nats.Connect(s.ClientURL(), createUserCreds(t, s, akp))
+	require_NoError(t, err)
+	defer ncs.Close()
+
+	const statsz = "STATSZ"
+	for _, test := range []struct {
+		name      string
+		f         func() string
+		expectTwo bool
+	}{
+		{"server stats ping request subject", func() string { return serverStatsPingReqSubj }, true},
+		{"server ping request subject", func() string { return fmt.Sprintf(serverPingReqSubj, statsz) }, true},
+		{"server direct request subject", func() string { return fmt.Sprintf(serverDirectReqSubj, s.ID(), statsz) }, false},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			// Clear all slow consumers values
+			s.scStats.clients.Store(0)
+			s.scStats.routes.Store(0)
+			s.scStats.gateways.Store(0)
+			s.scStats.leafs.Store(0)
+
+			msg, err := ncs.Request(test.f(), nil, time.Second)
+			require_NoError(t, err)
+
+			var ssm ServerStatsMsg
+			err = json.Unmarshal(msg.Data, &ssm)
+			require_NoError(t, err)
+
+			// No slow consumer stats, so should be nil
+			require_True(t, ssm.Stats.SlowConsumersStats == nil)
+
+			// Now set some values
+			s.scStats.clients.Store(1)
+			s.scStats.routes.Store(2)
+			s.scStats.gateways.Store(3)
+			s.scStats.leafs.Store(4)
+
+			msg, err = ncs.Request(test.f(), nil, time.Second)
+			require_NoError(t, err)
+
+			ssm = ServerStatsMsg{}
+			err = json.Unmarshal(msg.Data, &ssm)
+			require_NoError(t, err)
+
+			require_NotNil(t, ssm.Stats.SlowConsumersStats)
+			scs := ssm.Stats.SlowConsumersStats
+			require_Equal(t, scs.Clients, 1)
+			require_Equal(t, scs.Routes, 2)
+			require_Equal(t, scs.Gateways, 3)
+			require_Equal(t, scs.Leafs, 4)
+		})
+	}
+}
diff --git a/server/norace_test.go b/server/norace_test.go
index 7de9c949..78b62809 100644
--- a/server/norace_test.go
+++ b/server/norace_test.go
@@ -10811,21 +10811,24 @@ func TestNoRaceJetStreamStandaloneDontReplyToAckBeforeProcessingIt(t *testing.T)
 		for i := 0; i < total; i++ {
 			go func() {
 				defer wg.Done()
-				msgs, err := sub.Fetch(1)
-				if err != nil {
-					errCh <- err
-					return
-				}
-				msg := msgs[0]
-				err = msg.AckSync()
-				if err != nil {
-					errCh <- err
-					return
-				}
-				_, err = js.Publish(msg.Subject, []byte("hello"))
-				if err != nil {
-					errCh <- err
-					return
+				for {
+					msgs, err := sub.Fetch(1)
+					if err != nil {
+						time.Sleep(5 * time.Millisecond)
+						continue
+					}
+					msg := msgs[0]
+					err = msg.AckSync()
+					if err != nil {
+						time.Sleep(5 * time.Millisecond)
+						continue
+					}
+					_, err = js.Publish(msg.Subject, []byte("hello"))
+					if err != nil {
+						errCh <- err
+						return
+					}
+					break
 				}
 			}()
 		}