planner: introduce tidb_general_plan_cache_size for general plan cache

sessionctx/variable/sysvar.go

@@ -854,6 +854,15 @@ var defaultSysVars = []*SysVar{
 	}, GetGlobal: func(s *SessionVars) (string, error) {
 		return BoolToOnOff(EnableTmpStorageOnOOM.Load()), nil
 	}},
+	{Scope: ScopeGlobal, Name: TiDBGeneralPlanCacheSize, Value: strconv.FormatUint(uint64(DefTiDBGeneralPlanCacheSize), 10), Type: TypeUnsigned, MinValue: 0, MaxValue: 100000, SetGlobal: func(s *SessionVars, val string) error {
+		uVal, err := strconv.ParseUint(val, 10, 64)
+		if err == nil {
+			GeneralPlanCacheSize.Store(uVal)
+		}
+		return err
+	}, GetGlobal: func(s *SessionVars) (string, error) {
+		return strconv.FormatUint(GeneralPlanCacheSize.Load(), 10), nil
+	}},
 
 	/* The system variables below have GLOBAL and SESSION scope  */
 	{Scope: ScopeGlobal | ScopeSession, Name: TiDBRowFormatVersion, Value: strconv.Itoa(DefTiDBRowFormatV1), Type: TypeUnsigned, MinValue: 1, MaxValue: 2, SetGlobal: func(s *SessionVars, val string) error {

sessionctx/variable/sysvar_test.go

@@ -1159,3 +1159,25 @@ func TestSetTIDBDiskQuota(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, strconv.FormatInt(pb, 10), val)
 }
+
+func TestGeneralPlanCache(t *testing.T) {
+	vars := NewSessionVars()
+	mock := NewMockGlobalAccessor4Tests()
+	mock.SessionVars = vars
+	vars.GlobalVarsAccessor = mock
+	val, err := vars.GetGlobalSystemVar(TiDBGeneralPlanCacheSize)
+	require.NoError(t, err)
+	require.Equal(t, val, "100")
+	require.NoError(t, vars.GlobalVarsAccessor.SetGlobalSysVar(TiDBGeneralPlanCacheSize, "1000"))
+	val, err = vars.GetGlobalSystemVar(TiDBGeneralPlanCacheSize)
+	require.NoError(t, err)
+	require.Equal(t, val, "1000")
+	require.NoError(t, vars.GlobalVarsAccessor.SetGlobalSysVar(TiDBGeneralPlanCacheSize, "-1"))
+	val, err = vars.GetGlobalSystemVar(TiDBGeneralPlanCacheSize)
+	require.NoError(t, err)
+	require.Equal(t, val, "0")
+	require.NoError(t, vars.GlobalVarsAccessor.SetGlobalSysVar(TiDBGeneralPlanCacheSize, "1000000"))
+	val, err = vars.GetGlobalSystemVar(TiDBGeneralPlanCacheSize)
+	require.NoError(t, err)
+	require.Equal(t, val, "100000")
+}

sessionctx/variable/tidb_vars.go

@@ -791,6 +791,8 @@ const (
 	TiDBDDLEnableFastReorg = "tidb_ddl_fast_reorg"
 	// TiDBDDLDiskQuota used to set disk quota for lightning add index.
 	TiDBDDLDiskQuota = "tidb_ddl_disk_quota"
+	// TiDBGeneralPlanCacheSize controls the size of general plan cache. 0 indicate close.
+	TiDBGeneralPlanCacheSize = "tidb_general_plan_cache_size"
 )
 
 // TiDB intentional limits
@@ -1007,6 +1009,7 @@ const (
 	DefTiDBEnableFastReorg                         = false
 	DefTiDBDDLDiskQuota                            = 100 * 1024 * 1024 * 1024 // 100GB
 	DefExecutorConcurrency                         = 5
+	DefTiDBGeneralPlanCacheSize                    = 100
 	// MaxDDLReorgBatchSize is exported for testing.
 	MaxDDLReorgBatchSize           int32  = 10240
 	MinDDLReorgBatchSize           int32  = 32
@@ -1058,6 +1061,8 @@ var (
 	EnableFastReorg = atomic.NewBool(DefTiDBEnableFastReorg)
 	// DDLDiskQuota is the temporary variable for set disk quota for lightning
 	DDLDiskQuota = atomic.NewInt64(DefTiDBDDLDiskQuota)
+	// GeneralPlanCacheSize is a variable for general plan cache
+	GeneralPlanCacheSize = atomic.NewUint64(DefTiDBGeneralPlanCacheSize)
 )
 
 var (