variables: add constraints on tidb_super_read_only when tidb_restrict…

…ed_read_only is turned on (#31746) (#31842)

close #31745

domain/sysvar_cache.go

@@ -230,6 +230,8 @@ func (do *Domain) checkEnableServerGlobalVar(name, sVal string) {
 			break
 		}
 		topsqlstate.GlobalState.ReportIntervalSeconds.Store(val)
+	case variable.TiDBSuperReadOnly:
+		variable.VarTiDBSuperReadOnly.Store(variable.TiDBOptOn(sVal))
 	case variable.TiDBRestrictedReadOnly:
 		variable.RestrictedReadOnly.Store(variable.TiDBOptOn(sVal))
 	case variable.TiDBStoreLimit:

planner/optimize.go

@@ -346,7 +346,7 @@ func optimize(ctx context.Context, sctx sessionctx.Context, node ast.Node, is in
 		return nil, nil, 0, err
 	}
 
-	if !sctx.GetSessionVars().InRestrictedSQL && variable.RestrictedReadOnly.Load() {
+	if !sctx.GetSessionVars().InRestrictedSQL && variable.RestrictedReadOnly.Load() || variable.VarTiDBSuperReadOnly.Load() {
 		allowed, err := allowInReadOnlyMode(sctx, node)
 		if err != nil {
 			return nil, nil, 0, err

sessionctx/variable/sysvar.go

@@ -1132,7 +1132,33 @@ var defaultSysVars = []*SysVar{
 		errors.RedactLogEnabled.Store(s.EnableRedactLog)
 		return nil
 	}},
-	{Scope: ScopeGlobal, Name: TiDBRestrictedReadOnly, Value: BoolToOnOff(DefTiDBRestrictedReadOnly), Type: TypeBool},
+	{Scope: ScopeGlobal, Name: TiDBRestrictedReadOnly, Value: BoolToOnOff(DefTiDBRestrictedReadOnly), Type: TypeBool, SetGlobal: func(s *SessionVars, val string) error {
+		on := TiDBOptOn(val)
+		if on {
+			err := s.GlobalVarsAccessor.SetGlobalSysVar(TiDBSuperReadOnly, "ON")
+			if err != nil {
+				return err
+			}
+		}
+		RestrictedReadOnly.Store(on)
+		return nil
+	}},
+	{Scope: ScopeGlobal, Name: TiDBSuperReadOnly, Value: BoolToOnOff(DefTiDBSuperReadOnly), Type: TypeBool, Validation: func(vars *SessionVars, normalizedValue string, _ string, _ ScopeFlag) (string, error) {
+		on := TiDBOptOn(normalizedValue)
+		if !on {
+			result, err := vars.GlobalVarsAccessor.GetGlobalSysVar(TiDBRestrictedReadOnly)
+			if err != nil {
+				return normalizedValue, err
+			}
+			if TiDBOptOn(result) {
+				return normalizedValue, fmt.Errorf("can't turn off %s when %s is on", TiDBSuperReadOnly, TiDBRestrictedReadOnly)
+			}
+		}
+		return normalizedValue, nil
+	}, SetGlobal: func(s *SessionVars, val string) error {
+		VarTiDBSuperReadOnly.Store(TiDBOptOn(val))
+		return nil
+	}},
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBShardAllocateStep, Value: strconv.Itoa(DefTiDBShardAllocateStep), Type: TypeInt, MinValue: 1, MaxValue: uint64(math.MaxInt64), SetSession: func(s *SessionVars, val string) error {
 		s.ShardAllocateStep = tidbOptInt64(val, DefTiDBShardAllocateStep)
 		return nil

sessionctx/variable/sysvar_test.go

@@ -540,6 +540,43 @@ func TestIsNoop(t *testing.T) {
 	require.True(t, sv.IsNoop)
 }
 
+func TestTiDBReadOnly(t *testing.T) {
+	rro := GetSysVar(TiDBRestrictedReadOnly)
+	sro := GetSysVar(TiDBSuperReadOnly)
+
+	vars := NewSessionVars()
+	mock := NewMockGlobalAccessor4Tests()
+	mock.SessionVars = vars
+	vars.GlobalVarsAccessor = mock
+
+	// turn on tidb_restricted_read_only should turn on tidb_super_read_only
+	require.NoError(t, mock.SetGlobalSysVar(rro.Name, "ON"))
+	result, err := mock.GetGlobalSysVar(sro.Name)
+	require.NoError(t, err)
+	require.Equal(t, "ON", result)
+
+	// can't turn off tidb_super_read_only if tidb_restricted_read_only is on
+	err = mock.SetGlobalSysVar(sro.Name, "OFF")
+	require.Error(t, err)
+	require.Equal(t, "can't turn off tidb_super_read_only when tidb_restricted_read_only is on", err.Error())
+
+	// turn off tidb_restricted_read_only won't affect tidb_super_read_only
+	require.NoError(t, mock.SetGlobalSysVar(rro.Name, "OFF"))
+	result, err = mock.GetGlobalSysVar(rro.Name)
+	require.NoError(t, err)
+	require.Equal(t, "OFF", result)
+
+	result, err = mock.GetGlobalSysVar(sro.Name)
+	require.NoError(t, err)
+	require.Equal(t, "ON", result)
+
+	// it is ok to turn off tidb_super_read_only now
+	require.NoError(t, mock.SetGlobalSysVar(sro.Name, "OFF"))
+	result, err = mock.GetGlobalSysVar(sro.Name)
+	require.NoError(t, err)
+	require.Equal(t, "OFF", result)
+}
+
 func TestInstanceScopedVars(t *testing.T) {
 	// This tests instance scoped variables through GetSessionOrGlobalSystemVar().
 	// Eventually these should be changed to use getters so that the switch

sessionctx/variable/tidb_vars.go

@@ -533,6 +533,9 @@ const (
 	// TiDBRestrictedReadOnly is meant for the cloud admin to toggle the cluster read only
 	TiDBRestrictedReadOnly = "tidb_restricted_read_only"
 
+	// TiDBSuperReadOnly is tidb's variant of mysql's super_read_only, which has some differences from mysql's super_read_only.
+	TiDBSuperReadOnly = "tidb_super_read_only"
+
 	// TiDBShardAllocateStep indicates the max size of continuous rowid shard in one transaction.
 	TiDBShardAllocateStep = "tidb_shard_allocate_step"
 	// TiDBEnableTelemetry indicates that whether usage data report to PingCAP is enabled.
@@ -767,6 +770,7 @@ const (
 	DefTiDBEnableClusteredIndex           = ClusteredIndexDefModeIntOnly
 	DefTiDBRedactLog                      = false
 	DefTiDBRestrictedReadOnly             = false
+	DefTiDBSuperReadOnly                  = false
 	DefTiDBShardAllocateStep              = math.MaxInt64
 	DefTiDBEnableTelemetry                = true
 	DefTiDBEnableParallelApply            = false
@@ -823,6 +827,7 @@ var (
 	MaxTSOBatchWaitInterval               = atomic.NewFloat64(DefTiDBTSOClientBatchMaxWaitTime)
 	EnableTSOFollowerProxy                = atomic.NewBool(DefTiDBEnableTSOFollowerProxy)
 	RestrictedReadOnly                    = atomic.NewBool(DefTiDBRestrictedReadOnly)
+	VarTiDBSuperReadOnly                  = atomic.NewBool(DefTiDBSuperReadOnly)
 	PersistAnalyzeOptions                 = atomic.NewBool(DefTiDBPersistAnalyzeOptions)
 	EnableColumnTracking                  = atomic.NewBool(DefTiDBEnableColumnTracking)
 	StatsLoadSyncWait                     = atomic.NewInt64(DefTiDBStatsLoadSyncWait)

tests/readonlytest/go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/go-sql-driver/mysql v1.6.0
 	github.com/pingcap/tidb v2.0.11+incompatible
 	github.com/stretchr/testify v1.7.0
-	go.uber.org/goleak v1.1.11
+	go.uber.org/goleak v1.1.12
 )
 
 replace github.com/pingcap/tidb => ../../