add skip isolation level check variable (#10065)

Author: marsishandsome

executor/set_test.go

@@ -285,6 +285,49 @@ func (s *testSuite2) TestSetVar(c *C) {
 	c.Assert(err, NotNil)
 	_, err = tk.Exec("set global tidb_batch_commit = 2")
 	c.Assert(err, NotNil)
+
+	// test skip isolation level check: init
+	tk.MustExec("SET GLOBAL tidb_skip_isolation_level_check = 0")
+	tk.MustExec("SET SESSION tidb_skip_isolation_level_check = 0")
+	tk.MustExec("SET GLOBAL TRANSACTION ISOLATION LEVEL READ COMMITTED")
+	tk.MustExec("SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED")
+	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
+
+	// test skip isolation level check: error
+	_, err = tk.Exec("SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedIsolationLevel), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
+
+	_, err = tk.Exec("SET GLOBAL TRANSACTION ISOLATION LEVEL SERIALIZABLE")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedIsolationLevel), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
+
+	// test skip isolation level check: success
+	tk.MustExec("SET GLOBAL tidb_skip_isolation_level_check = 1")
+	tk.MustExec("SET SESSION tidb_skip_isolation_level_check = 1")
+	tk.MustExec("SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE")
+	tk.MustQuery("show warnings").Check(testkit.Rows(
+		"Warning 1105 The isolation level 'SERIALIZABLE' is not supported. Set tidb_skip_isolation_level_check=1 to skip this error"))
+	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("SERIALIZABLE"))
+	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("SERIALIZABLE"))
+
+	// test skip isolation level check: success
+	tk.MustExec("SET GLOBAL tidb_skip_isolation_level_check = 0")
+	tk.MustExec("SET SESSION tidb_skip_isolation_level_check = 1")
+	tk.MustExec("SET GLOBAL TRANSACTION ISOLATION LEVEL READ UNCOMMITTED")
+	tk.MustQuery("show warnings").Check(testkit.Rows(
+		"Warning 1105 The isolation level 'READ-UNCOMMITTED' is not supported. Set tidb_skip_isolation_level_check=1 to skip this error"))
+	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
+	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
+
+	// test skip isolation level check: reset
+	tk.MustExec("SET GLOBAL tidb_skip_isolation_level_check = 0")
+	tk.MustExec("SET SESSION tidb_skip_isolation_level_check = 0")
 }
 
 func (s *testSuite2) TestSetCharset(c *C) {
@@ -584,6 +627,8 @@ func (s *testSuite2) TestValidateSetVar(c *C) {
 	result = tk.MustQuery("select @@tx_isolation;")
 	result.Check(testkit.Rows("REPEATABLE-READ"))
 
+	tk.MustExec("SET GLOBAL tidb_skip_isolation_level_check = 0")
+	tk.MustExec("SET SESSION tidb_skip_isolation_level_check = 0")
 	_, err = tk.Exec("set @@tx_isolation='SERIALIZABLE'")
 	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
 }

sessionctx/variable/session.go

@@ -603,7 +603,21 @@ func (s *SessionVars) SetSystemVar(name string, val string) error {
 	case TxnIsolationOneShot:
 		switch val {
 		case "SERIALIZABLE", "READ-UNCOMMITTED":
-			return ErrUnsupportedValueForVar.GenWithStackByArgs(name, val)
+			skipIsolationLevelCheck, err := GetSessionSystemVar(s, TiDBSkipIsolationLevelCheck)
+			returnErr := ErrUnsupportedIsolationLevel.GenWithStackByArgs(val)
+			if err != nil {
+				returnErr = err
+			}
+			if !TiDBOptOn(skipIsolationLevelCheck) || err != nil {
+				return returnErr
+			}
+			//SET TRANSACTION ISOLATION LEVEL will affect two internal variables:
+			// 1. tx_isolation
+			// 2. transaction_isolation
+			// The following if condition is used to deduplicate two same warnings.
+			if name == "transaction_isolation" {
+				s.StmtCtx.AppendWarning(returnErr)
+			}
 		}
 		s.TxnIsolationLevelOneShot.State = 1
 		s.TxnIsolationLevelOneShot.Value = val

sessionctx/variable/sysvar.go

@@ -85,6 +85,7 @@ var (
 	ErrTruncatedWrongValue         = terror.ClassVariable.New(CodeTruncatedWrongValue, mysql.MySQLErrName[mysql.ErrTruncatedWrongValue])
 	ErrMaxPreparedStmtCountReached = terror.ClassVariable.New(CodeMaxPreparedStmtCountReached, mysql.MySQLErrName[mysql.ErrMaxPreparedStmtCountReached])
 	ErrUnsupportedValueForVar      = terror.ClassVariable.New(CodeUnknownStatusVar, "variable '%s' does not yet support value: %s")
+	ErrUnsupportedIsolationLevel   = terror.ClassVariable.New(CodeUnknownStatusVar, "The isolation level '%s' is not supported. Set tidb_skip_isolation_level_check=1 to skip this error")
 )
 
 func init() {
@@ -673,6 +674,7 @@ var defaultSysVars = []*SysVar{
 	{ScopeSession, TiDBOptimizerSelectivityLevel, strconv.Itoa(DefTiDBOptimizerSelectivityLevel)},
 	{ScopeGlobal | ScopeSession, TiDBEnableWindowFunction, BoolToIntStr(DefEnableWindowFunction)},
 	{ScopeGlobal | ScopeSession, TiDBEnableFastAnalyze, BoolToIntStr(DefTiDBUseFastAnalyze)},
+	{ScopeGlobal | ScopeSession, TiDBSkipIsolationLevelCheck, BoolToIntStr(DefTiDBSkipIsolationLevelCheck)},
 	/* The following variable is defined as session scope but is actually server scope. */
 	{ScopeSession, TiDBGeneralLog, strconv.Itoa(DefTiDBGeneralLog)},
 	{ScopeSession, TiDBSlowLogThreshold, strconv.Itoa(logutil.DefaultSlowThreshold)},

sessionctx/variable/tidb_vars.go

@@ -131,6 +131,10 @@ const (
 
 	// TiDBCheckMb4ValueInUTF8 is used to control whether to enable the check wrong utf8 value.
 	TiDBCheckMb4ValueInUTF8 = "tidb_check_mb4_value_in_utf8"
+
+	// tidb_skip_isolation_level_check is used to control whether to return error when set unsupported transaction
+	// isolation level.
+	TiDBSkipIsolationLevelCheck = "tidb_skip_isolation_level_check"
 )
 
 // TiDB system variable names that both in session and global scope.
@@ -295,6 +299,7 @@ const (
 	DefEnableWindowFunction          = false
 	DefTiDBDDLSlowOprThreshold       = 300
 	DefTiDBUseFastAnalyze            = false
+	DefTiDBSkipIsolationLevelCheck   = false
 )
 
 // Process global variables.

sessionctx/variable/varsutil.go

@@ -429,7 +429,21 @@ func ValidateSetSystemVar(vars *SessionVars, name string, value string) (string,
 		}
 		switch upVal {
 		case "SERIALIZABLE", "READ-UNCOMMITTED":
-			return "", ErrUnsupportedValueForVar.GenWithStackByArgs(name, value)
+			skipIsolationLevelCheck, err := GetSessionSystemVar(vars, TiDBSkipIsolationLevelCheck)
+			returnErr := ErrUnsupportedIsolationLevel.GenWithStackByArgs(value)
+			if err != nil {
+				returnErr = err
+			}
+			if !TiDBOptOn(skipIsolationLevelCheck) || err != nil {
+				return "", returnErr
+			}
+			//SET TRANSACTION ISOLATION LEVEL will affect two internal variables:
+			// 1. tx_isolation
+			// 2. transaction_isolation
+			// The following if condition is used to deduplicate two same warnings.
+			if name == "transaction_isolation" {
+				vars.StmtCtx.AppendWarning(returnErr)
+			}
 		}
 		return upVal, nil
 	case TiDBInitChunkSize: