WIP

planner/core/optimizer.go

@@ -15,6 +15,7 @@ package core
 
 import (
 	"context"
+	"github.com/pingcap/tidb/planner/util"
 	"math"
 
 	"github.com/pingcap/errors"
@@ -136,15 +137,31 @@ func DoOptimize(ctx context.Context, sctx sessionctx.Context, flag uint64, logic
 	if err != nil {
 		return nil, 0, err
 	}
-	finalPlan := postOptimize(sctx, physical)
-	return finalPlan, cost, nil
+	finalPlan, err := postOptimize(sctx, physical)
+	return finalPlan, cost, err
 }
 
-func postOptimize(sctx sessionctx.Context, plan PhysicalPlan) PhysicalPlan {
+func postOptimize(sctx sessionctx.Context, plan PhysicalPlan) (PhysicalPlan, error) {
 	plan = eliminatePhysicalProjection(plan)
 	plan = injectExtraProjection(plan)
 	plan = eliminateUnionScanAndLock(sctx, plan)
-	return plan
+	return stabilizeResults(sctx, plan)
+}
+
+func stabilizeResults(sctx sessionctx.Context, plan PhysicalPlan) (PhysicalPlan, error) {
+	if !sctx.GetSessionVars().EnableStableResults {
+		return plan, nil
+	}
+	cols := plan.Schema().Columns
+	items := property.ItemsFromCols(cols, false)
+	byItems := make([]*util.ByItems, 0, len(cols))
+	for _, col := range cols {
+		byItems = append(byItems, &util.ByItems{Expr: col})
+	}
+	sortReqProp := &property.PhysicalProperty{TaskTp: property.RootTaskType, Items: items, ExpectedCnt: math.MaxFloat64}
+	sort := PhysicalSort{ByItems: byItems}.Init(sctx, plan.Stats(), 0, sortReqProp)
+	sort.SetChildren(plan)
+	return sort, sort.ResolveIndices()
 }
 
 func logicalOptimize(ctx context.Context, flag uint64, logic LogicalPlan) (LogicalPlan, error) {

session/session.go

@@ -1993,6 +1993,7 @@ var builtinGlobalVariable = []string{
 	variable.TiDBRedactLog,
 	variable.TiDBEnableTelemetry,
 	variable.TiDBEnableAmendPessimisticTxn,
+	variable.TiDBEnableStableResults,
 }
 
 var (

sessionctx/variable/session.go

@@ -639,6 +639,9 @@ type SessionVars struct {
 
 	// EnableAmendPessimisticTxn indicates if schema change amend is enabled for pessimistic transactions.
 	EnableAmendPessimisticTxn bool
+
+	// EnableStableResults if stabilize query results.
+	EnableStableResults bool
 }
 
 // PreparedParams contains the parameters of the current prepared statement when executing it.
@@ -1348,6 +1351,8 @@ func (s *SessionVars) SetSystemVar(name string, val string) error {
 		config.SetRedactLog(TiDBOptOn(val))
 	case TiDBEnableAmendPessimisticTxn:
 		s.EnableAmendPessimisticTxn = TiDBOptOn(val)
+	case TiDBEnableStableResults:
+		s.EnableStableResults = TiDBOptOn(val)
 	}
 	s.systems[name] = val
 	return nil

sessionctx/variable/sysvar.go

@@ -729,6 +729,7 @@ var defaultSysVars = []*SysVar{
 	{ScopeGlobal, TiDBRedactLog, strconv.Itoa(config.DefTiDBRedactLog)},
 	{ScopeGlobal, TiDBEnableTelemetry, BoolToIntStr(DefTiDBEnableTelemetry)},
 	{ScopeGlobal | ScopeSession, TiDBEnableAmendPessimisticTxn, boolToOnOff(DefTiDBEnableAmendPessimisticTxn)},
+	{ScopeGlobal | ScopeSession, TiDBEnableStableResults, BoolToIntStr(DefTiDBEnableStableResults)},
 }
 
 // SynonymsSysVariables is synonyms of system variables.

sessionctx/variable/tidb_vars.go

@@ -415,6 +415,9 @@ const (
 
 	// TiDBEnableAmendPessimisticTxn indicates if amend pessimistic transactions is enabled.
 	TiDBEnableAmendPessimisticTxn = "tidb_enable_amend_pessimistic_txn"
+
+	// TiDBEnableStableResults indicates if stabilize query results.
+	TiDBEnableStableResults = "tidb_enable_stable_results"
 )
 
 // Default TiDB system variable values.
@@ -516,6 +519,7 @@ const (
 	DefTiDBAllowAutoRandExplicitInsert = false
 	DefTiDBEnableTelemetry             = true
 	DefTiDBEnableAmendPessimisticTxn   = false
+	DefTiDBEnableStableResults         = false
 )
 
 // Process global variables.

sessionctx/variable/varsutil.go

@@ -448,7 +448,7 @@ func ValidateSetSystemVar(vars *SessionVars, name string, value string, scope Sc
 		TiDBCheckMb4ValueInUTF8, TiDBEnableSlowLog, TiDBRecordPlanInSlowLog,
 		TiDBScatterRegion, TiDBGeneralLog, TiDBConstraintCheckInPlace,
 		TiDBEnableVectorizedExpression, TiDBFoundInPlanCache, TiDBEnableCollectExecutionInfo,
-		TiDBAllowAutoRandExplicitInsert, TiDBEnableTelemetry, TiDBEnableAmendPessimisticTxn:
+		TiDBAllowAutoRandExplicitInsert, TiDBEnableTelemetry, TiDBEnableAmendPessimisticTxn, TiDBEnableStableResults:
 		fallthrough
 	case GeneralLog, AvoidTemporalUpgrade, BigTables, CheckProxyUsers, LogBin,
 		CoreFile, EndMakersInJSON, SQLLogBin, OfflineMode, PseudoSlaveMode, LowPriorityUpdates,