server: add counter for keys locking numbers(#14625)

executor/adapter.go

@@ -223,6 +223,10 @@ func (a *ExecStmt) Exec(ctx context.Context) (_ sqlexec.RecordSet, err error) {
 			if a.retryCount > 0 {
 				metrics.StatementPessimisticRetryCount.Observe(float64(a.retryCount))
 			}
+			lockKeysCnt := a.Ctx.GetSessionVars().StmtCtx.LockKeysCount
+			if lockKeysCnt > 0 {
+				metrics.StatementLockKeysCount.Add(float64(lockKeysCnt))
+			}
 			return
 		}
 		if str, ok := r.(string); !ok || !strings.HasPrefix(str, memory.PanicMemoryExceed) {

executor/executor.go

@@ -797,6 +797,7 @@ func newLockCtx(seVars *variable.SessionVars, lockWaitTime int64) *kv.LockCtx {
 		WaitStartTime:         seVars.StmtCtx.GetLockWaitStartTime(),
 		PessimisticLockWaited: &seVars.StmtCtx.PessimisticLockWaited,
 		LockKeysDuration:      &seVars.StmtCtx.LockKeysDuration,
+		LockKeysCount:         &seVars.StmtCtx.LockKeysCount,
 	}
 }
 

kv/kv.go

@@ -181,6 +181,7 @@ type LockCtx struct {
 	WaitStartTime         time.Time
 	PessimisticLockWaited *int32
 	LockKeysDuration      *time.Duration
+	LockKeysCount         *int32
 }
 
 // Client is used to send request to KV layer.

metrics/metrics.go

@@ -135,6 +135,7 @@ func RegisterMetrics() {
 	prometheus.MustRegister(TransactionDuration)
 	prometheus.MustRegister(StatementDeadlockDetectDuration)
 	prometheus.MustRegister(StatementPessimisticRetryCount)
+	prometheus.MustRegister(StatementLockKeysCount)
 	prometheus.MustRegister(UpdateSelfVersionHistogram)
 	prometheus.MustRegister(UpdateStatsCounter)
 	prometheus.MustRegister(WatchOwnerCounter)

metrics/session.go

@@ -116,6 +116,14 @@ var (
 			Help:      "Bucketed historgram of statement pessimistic retry count",
 			Buckets:   prometheus.ExponentialBuckets(1, 1.5, 14), // 1 ~ 291
 		})
+
+	StatementLockKeysCount = prometheus.NewCounter(
+		prometheus.CounterOpts{
+			Namespace: "tidb",
+			Subsystem: "session",
+			Name:      "statement_lock_keys_count",
+			Help:      "Keys locking for a single statement",
+		})
 )
 
 // Label constants.

sessionctx/stmtctx/stmtctx.go

@@ -139,6 +139,7 @@ type StatementContext struct {
 	// planNormalized use for cache the normalized plan, avoid duplicate builds.
 	planNormalized string
 	planDigest     string
+	LockKeysCount  int32
 }
 
 // GetNowTsCached getter for nowTs, if not set get now time and cache it

store/tikv/txn.go

@@ -352,6 +352,7 @@ func (txn *tikvTxn) rollbackPessimisticLocks() error {
 func (txn *tikvTxn) LockKeys(ctx context.Context, lockCtx *kv.LockCtx, keysInput ...kv.Key) error {
 	// Exclude keys that are already locked.
 	var err error
+	keys := make([][]byte, 0, len(keysInput))
 	defer func() {
 		if err == nil {
 			if lockCtx.PessimisticLockWaited != nil {
@@ -362,8 +363,10 @@ func (txn *tikvTxn) LockKeys(ctx context.Context, lockCtx *kv.LockCtx, keysInput
 				}
 			}
 		}
+		if lockCtx.LockKeysCount != nil {
+			*lockCtx.LockKeysCount += int32(len(keys))
+		}
 	}()
-	keys := make([][]byte, 0, len(keysInput))
 	txn.mu.Lock()
 	for _, key := range keysInput {
 		if _, ok := txn.lockedMap[string(key)]; !ok {