*: add tidb_enable_noop_functions to default disable get_lock()/release_lock() (#10987)

* issue#4100 add new variable to default disable usage of get_lock and release_lock functions

Author: cfzjywxk

executor/set_test.go

@@ -20,6 +20,7 @@ import (
 	. "github.com/pingcap/check"
 	"github.com/pingcap/parser/terror"
 	"github.com/pingcap/tidb/config"
+	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/sessionctx/variable"
 	"github.com/pingcap/tidb/util/testkit"
@@ -741,3 +742,45 @@ func (s *testSuite2) TestSelectGlobalVar(c *C) {
 	err = tk.ExecToErr("select @@global.invalid")
 	c.Assert(terror.ErrorEqual(err, variable.UnknownSystemVar), IsTrue, Commentf("err %v", err))
 }
+
+func (s *testSuite2) TestEnableNoopFunctionsVar(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+
+	// test for tidb_enable_noop_functions
+	tk.MustQuery(`select @@global.tidb_enable_noop_functions;`).Check(testkit.Rows("0"))
+	tk.MustQuery(`select @@tidb_enable_noop_functions;`).Check(testkit.Rows("0"))
+
+	_, err := tk.Exec(`select get_lock('lock1', 2);`)
+	c.Assert(terror.ErrorEqual(err, expression.ErrFunctionsNoopImpl), IsTrue, Commentf("err %v", err))
+	_, err = tk.Exec(`select release_lock('lock1');`)
+	c.Assert(terror.ErrorEqual(err, expression.ErrFunctionsNoopImpl), IsTrue, Commentf("err %v", err))
+
+	// change session var to 1
+	tk.MustExec(`set tidb_enable_noop_functions=1;`)
+	tk.MustQuery(`select @@tidb_enable_noop_functions;`).Check(testkit.Rows("1"))
+	tk.MustQuery(`select @@global.tidb_enable_noop_functions;`).Check(testkit.Rows("0"))
+	tk.MustQuery(`select get_lock("lock", 10)`).Check(testkit.Rows("1"))
+	tk.MustQuery(`select release_lock("lock")`).Check(testkit.Rows("1"))
+
+	// restore to 0
+	tk.MustExec(`set tidb_enable_noop_functions=0;`)
+	tk.MustQuery(`select @@tidb_enable_noop_functions;`).Check(testkit.Rows("0"))
+	tk.MustQuery(`select @@global.tidb_enable_noop_functions;`).Check(testkit.Rows("0"))
+
+	_, err = tk.Exec(`select get_lock('lock2', 10);`)
+	c.Assert(terror.ErrorEqual(err, expression.ErrFunctionsNoopImpl), IsTrue, Commentf("err %v", err))
+	_, err = tk.Exec(`select release_lock('lock2');`)
+	c.Assert(terror.ErrorEqual(err, expression.ErrFunctionsNoopImpl), IsTrue, Commentf("err %v", err))
+
+	// set test
+	_, err = tk.Exec(`set tidb_enable_noop_functions='abc'`)
+	c.Assert(err, NotNil)
+	_, err = tk.Exec(`set tidb_enable_noop_functions=11`)
+	c.Assert(err, NotNil)
+	tk.MustExec(`set tidb_enable_noop_functions="off";`)
+	tk.MustQuery(`select @@tidb_enable_noop_functions;`).Check(testkit.Rows("off"))
+	tk.MustExec(`set tidb_enable_noop_functions="on";`)
+	tk.MustQuery(`select @@tidb_enable_noop_functions;`).Check(testkit.Rows("on"))
+	tk.MustExec(`set tidb_enable_noop_functions=0;`)
+	tk.MustQuery(`select @@tidb_enable_noop_functions;`).Check(testkit.Rows("0"))
+}

expression/errors.go

@@ -28,6 +28,7 @@ var (
 	ErrRegexp                  = terror.ClassExpression.New(mysql.ErrRegexp, mysql.MySQLErrName[mysql.ErrRegexp])
 	ErrOperandColumns          = terror.ClassExpression.New(mysql.ErrOperandColumns, mysql.MySQLErrName[mysql.ErrOperandColumns])
 	ErrCutValueGroupConcat     = terror.ClassExpression.New(mysql.ErrCutValueGroupConcat, mysql.MySQLErrName[mysql.ErrCutValueGroupConcat])
+	ErrFunctionsNoopImpl       = terror.ClassExpression.New(mysql.ErrNotSupportedYet, "function %s has only noop implementation in tidb now, use tidb_enable_noop_functions to enable these functions")
 
 	// All the un-exported errors are defined here:
 	errFunctionNotExists             = terror.ClassExpression.New(mysql.ErrSpDoesNotExist, mysql.MySQLErrName[mysql.ErrSpDoesNotExist])

expression/function_traits.go

@@ -156,3 +156,11 @@ var mutableEffectsFunctions = map[string]struct{}{
 	ast.GetVar:      {},
 	ast.AnyValue:    {},
 }
+
+// some functions like "get_lock" and "release_lock" currently do NOT have
+// right implementations, but may have noop ones(like with any inputs, always return 1)
+// if apps really need these "funcs" to run, we offer sys var(tidb_enable_noop_functions) to enable noop usage
+var noopFuncs = map[string]struct{}{
+	ast.GetLock:     {},
+	ast.ReleaseLock: {},
+}

expression/integration_test.go

@@ -202,6 +202,7 @@ func (s *testIntegrationSuite) TestMiscellaneousBuiltin(c *C) {
 	tk.MustQuery("select a,any_value(b),sum(c) from t1 group by a order by a;").Check(testkit.Rows("1 10 0", "2 30 0"))
 
 	// for locks
+	tk.MustExec(`set tidb_enable_noop_functions=1;`)
 	result := tk.MustQuery(`SELECT GET_LOCK('test_lock1', 10);`)
 	result.Check(testkit.Rows("1"))
 	result = tk.MustQuery(`SELECT GET_LOCK('test_lock2', 10);`)

expression/scalar_function.go

@@ -82,6 +82,11 @@ func newFunctionImpl(ctx sessionctx.Context, fold bool, funcName string, retType
 	if !ok {
 		return nil, errFunctionNotExists.GenWithStackByArgs("FUNCTION", funcName)
 	}
+	if !ctx.GetSessionVars().EnableNoopFuncs {
+		if _, ok := noopFuncs[funcName]; ok {
+			return nil, ErrFunctionsNoopImpl.GenWithStackByArgs(funcName)
+		}
+	}
 	funcArgs := make([]Expression, len(args))
 	copy(funcArgs, args)
 	f, err := fc.getFunction(ctx, funcArgs)

expression/typeinfer_test.go

@@ -103,6 +103,7 @@ func (s *testInferTypeSuite) TestInferType(c *C) {
 		c_year year
 	)`
 	testKit.MustExec(sql)
+	testKit.MustExec(`set tidb_enable_noop_functions=1;`)
 
 	var tests []typeInferTestCase
 	tests = append(tests, s.createTestCase4Constants()...)

session/session.go

@@ -1697,6 +1697,7 @@ var builtinGlobalVariable = []string{
 	variable.TiDBEnableWindowFunction,
 	variable.TiDBEnableFastAnalyze,
 	variable.TiDBExpensiveQueryTimeThreshold,
+	variable.TiDBEnableNoopFuncs,
 	variable.TiDBEnableIndexMerge,
 }
 

sessionctx/variable/session.go

@@ -395,6 +395,9 @@ type SessionVars struct {
 
 	// ConnectionInfo indicates current connection info used by current session, only be lazy assigned by plugin.
 	ConnectionInfo *ConnectionInfo
+
+	// use noop funcs or not
+	EnableNoopFuncs bool
 }
 
 // ConnectionInfo present connection used by audit.
@@ -448,6 +451,7 @@ func NewSessionVars() *SessionVars {
 		WaitSplitRegionFinish:       DefTiDBWaitSplitRegionFinish,
 		WaitSplitRegionTimeout:      DefWaitSplitRegionTimeout,
 		EnableIndexMerge:            false,
+		EnableNoopFuncs:             DefTiDBEnableNoopFuncs,
 	}
 	vars.Concurrency = Concurrency{
 		IndexLookupConcurrency:     DefIndexLookupConcurrency,
@@ -824,6 +828,8 @@ func (s *SessionVars) SetSystemVar(name string, val string) error {
 		s.LowResolutionTSO = TiDBOptOn(val)
 	case TiDBEnableIndexMerge:
 		s.EnableIndexMerge = TiDBOptOn(val)
+	case TiDBEnableNoopFuncs:
+		s.EnableNoopFuncs = TiDBOptOn(val)
 	}
 	s.systems[name] = val
 	return nil

sessionctx/variable/sysvar.go

@@ -702,6 +702,7 @@ var defaultSysVars = []*SysVar{
 	{ScopeSession, TiDBWaitSplitRegionTimeout, strconv.Itoa(DefWaitSplitRegionTimeout)},
 	{ScopeSession, TiDBLowResolutionTSO, "0"},
 	{ScopeSession, TiDBExpensiveQueryTimeThreshold, strconv.Itoa(DefTiDBExpensiveQueryTimeThreshold)},
+	{ScopeGlobal | ScopeSession, TiDBEnableNoopFuncs, BoolToIntStr(DefTiDBEnableNoopFuncs)},
 }
 
 // SynonymsSysVariables is synonyms of system variables.

sessionctx/variable/tidb_vars.go

@@ -280,6 +280,9 @@ const (
 
 	// TiDBEnableIndexMerge indicates to generate IndexMergePath.
 	TiDBEnableIndexMerge = "tidb_enable_index_merge"
+
+	// TiDBEnableNoopFuncs set true will enable using fake funcs(like get_lock release_lock)
+	TiDBEnableNoopFuncs = "tidb_enable_noop_functions"
 )
 
 // Default TiDB system variable values.
@@ -342,6 +345,7 @@ const (
 	DefTiDBExpensiveQueryTimeThreshold = 60 // 60s
 	DefTiDBWaitSplitRegionFinish       = true
 	DefWaitSplitRegionTimeout          = 300 // 300s
+	DefTiDBEnableNoopFuncs             = false
 )
 
 // Process global variables.