*: add an option to enable pessimistic mode for auto-commit transacti…

…ons (#32056)

close #31135

config/config.go

@@ -569,6 +569,8 @@ type PessimisticTxn struct {
 	DeadlockHistoryCapacity uint `toml:"deadlock-history-capacity" json:"deadlock-history-capacity"`
 	// Whether retryable deadlocks (in-statement deadlocks) are collected to the information_schema.deadlocks table.
 	DeadlockHistoryCollectRetryable bool `toml:"deadlock-history-collect-retryable" json:"deadlock-history-collect-retryable"`
+	// PessimisticAutoCommit represents if true it means the auto-commit transactions will be in pessimistic mode.
+	PessimisticAutoCommit AtomicBool `toml:"pessimistic-auto-commit" json:"pessimistic-auto-commit"`
 }
 
 // DefaultPessimisticTxn returns the default configuration for PessimisticTxn
@@ -577,6 +579,7 @@ func DefaultPessimisticTxn() PessimisticTxn {
 		MaxRetryCount:                   256,
 		DeadlockHistoryCapacity:         10,
 		DeadlockHistoryCollectRetryable: false,
+		PessimisticAutoCommit:           *NewAtomicBool(false),
 	}
 }
 

config/config.toml.example

@@ -460,6 +460,9 @@ deadlock-history-capacity = 10
 # Whether retryable deadlocks (in-statement deadlocks) are collected to the information_schema.deadlocks table.
 deadlock-history-collect-retryable = false
 
+# If true it means the auto-commit transactions will be in pessimistic mode.
+pessimistic-auto-commit = false
+
 # experimental section controls the features that are still experimental: their semantics,
 # interfaces are subject to change, using these features in the production environment is not recommended.
 [experimental]

config/config_test.go

@@ -252,6 +252,7 @@ spilled-file-encryption-method = "plaintext"
 [pessimistic-txn]
 deadlock-history-capacity = 123
 deadlock-history-collect-retryable = true
+pessimistic-auto-commit = true
 [top-sql]
 receiver-address = "127.0.0.1:10100"
 [status]
@@ -308,6 +309,7 @@ grpc-max-send-msg-size = 40960
 	require.Equal(t, uint64(30), conf.StoresRefreshInterval)
 	require.Equal(t, uint(123), conf.PessimisticTxn.DeadlockHistoryCapacity)
 	require.True(t, conf.PessimisticTxn.DeadlockHistoryCollectRetryable)
+	require.True(t, conf.PessimisticTxn.PessimisticAutoCommit.Load())
 	require.Equal(t, "127.0.0.1:10100", conf.TopSQL.ReceiverAddress)
 	require.True(t, conf.Experimental.AllowsExpressionIndex)
 	require.Equal(t, uint(20), conf.Status.GRPCKeepAliveTime)
@@ -643,7 +645,7 @@ func TestSecurityValid(t *testing.T) {
 
 func TestTcpNoDelay(t *testing.T) {
 	c1 := NewConfig()
-	//check default value
+	// check default value
 	require.True(t, c1.Performance.TCPNoDelay)
 }
 

session/pessimistic_test.go

@@ -2360,7 +2360,7 @@ func (s *testPessimisticSuite) TestIssue21498(c *C) {
 	tk.MustExec("set tidb_enable_amend_pessimistic_txn = 1")
 
 	for _, partition := range []bool{false, true} {
-		//RC test
+		// RC test
 		tk.MustExec("drop table if exists t, t1")
 		createTable := "create table t (id int primary key, v int, index iv (v))"
 		if partition {
@@ -2529,7 +2529,7 @@ func (s *testPessimisticSuite) TestPlanCacheSchemaChange(c *C) {
 	tk.MustExec("set tidb_enable_amend_pessimistic_txn = 1")
 	tk2.MustExec("set tidb_enable_amend_pessimistic_txn = 1")
 
-	//generate plan cache
+	// generate plan cache
 	tk.MustExec("prepare update_stmt from 'update t set vv = vv + 1 where v = ?'")
 	tk.MustExec("set @v = 1")
 	tk.MustExec("execute update_stmt using @v")
@@ -2836,3 +2836,29 @@ func (s *testPessimisticSuite) TestAmendForColumnChange(c *C) {
 
 	tk2.MustExec("drop database test_db")
 }
+
+func (s *testPessimisticSuite) TestPessimisticAutoCommitTxn(c *C) {
+	tk := testkit.NewTestKitWithInit(c, s.store)
+	tk.MustExec("set tidb_txn_mode = 'pessimistic'")
+	tk.MustExec("drop database if exists test_db")
+	tk.MustExec("create database test_db")
+	tk.MustExec("use test_db")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t (i int)")
+	tk.MustExec("insert into t values (1)")
+	tk.MustExec("set autocommit = on")
+
+	rows := tk.MustQuery("explain update t set i = -i").Rows()
+	explain := fmt.Sprintf("%v", rows[1])
+	c.Assert(explain, Not(Matches), ".*SelectLock.*")
+
+	originCfg := config.GetGlobalConfig()
+	defer config.StoreGlobalConfig(originCfg)
+	newCfg := *originCfg
+	newCfg.PessimisticTxn.PessimisticAutoCommit.Store(true)
+	config.StoreGlobalConfig(&newCfg)
+
+	rows = tk.MustQuery("explain update t set i = -i").Rows()
+	explain = fmt.Sprintf("%v", rows[1])
+	c.Assert(explain, Matches, ".*SelectLock.*")
+}

session/session.go

@@ -3085,7 +3085,8 @@ func (s *session) PrepareTxnCtx(ctx context.Context) error {
 		ShardStep:  int(s.sessionVars.ShardAllocateStep),
 		TxnScope:   s.GetSessionVars().CheckAndGetTxnScope(),
 	}
-	if !s.sessionVars.IsAutocommit() || s.sessionVars.RetryInfo.Retrying {
+	if !s.sessionVars.IsAutocommit() || s.sessionVars.RetryInfo.Retrying ||
+		config.GetGlobalConfig().PessimisticTxn.PessimisticAutoCommit.Load() {
 		if s.sessionVars.TxnMode == ast.Pessimistic {
 			s.sessionVars.TxnCtx.IsPessimistic = true
 		}