From 77f7f9dab7fc9a511db8ce29179abcc4130d0eb6 Mon Sep 17 00:00:00 2001
From: ti-srebot <66930949+ti-srebot@users.noreply.github.com>
Date: Wed, 10 Aug 2022 11:36:48 +0800
Subject: [PATCH] executor: prevent sending cop request for show columns
 (#36613) (#36817)

close pingcap/tidb#36426, ref pingcap/tidb#36496
---
 executor/show.go                    |  3 ++-
 planner/core/expression_rewriter.go |  4 ++--
 planner/core/planbuilder.go         | 23 +++++++++++++++++++++--
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/executor/show.go b/executor/show.go
index 5f1b3f8bad927..8bcc2a7bd5bb0 100644
--- a/executor/show.go
+++ b/executor/show.go
@@ -1885,7 +1885,8 @@ func (e *ShowExec) fetchShowBuiltins() error {
 func tryFillViewColumnType(ctx context.Context, sctx sessionctx.Context, is infoschema.InfoSchema, dbName model.CIStr, tbl *model.TableInfo) error {
 	if tbl.IsView() {
 		// Retrieve view columns info.
-		planBuilder, _ := plannercore.NewPlanBuilder().Init(sctx, is, &hint.BlockHintProcessor{})
+		planBuilder, _ := plannercore.NewPlanBuilder(
+			plannercore.PlanBuilderOptNoExecution{}).Init(sctx, is, &hint.BlockHintProcessor{})
 		if viewLogicalPlan, err := planBuilder.BuildDataSourceFromView(ctx, dbName, tbl); err == nil {
 			viewSchema := viewLogicalPlan.Schema()
 			viewOutputNames := viewLogicalPlan.OutputNames()
diff --git a/planner/core/expression_rewriter.go b/planner/core/expression_rewriter.go
index c088e0f48d582..1071d5fd6ebc4 100644
--- a/planner/core/expression_rewriter.go
+++ b/planner/core/expression_rewriter.go
@@ -816,7 +816,7 @@ func (er *expressionRewriter) handleExistSubquery(ctx context.Context, v *ast.Ex
 		return v, true
 	}
 	np = er.popExistsSubPlan(np)
-	if len(ExtractCorrelatedCols4LogicalPlan(np)) > 0 {
+	if er.b.disableSubQueryPreprocessing || len(ExtractCorrelatedCols4LogicalPlan(np)) > 0 {
 		er.p, er.err = er.b.buildSemiApply(er.p, np, nil, er.asScalar, v.Not)
 		if er.err != nil || !er.asScalar {
 			return v, true
@@ -991,7 +991,7 @@ func (er *expressionRewriter) handleScalarSubquery(ctx context.Context, v *ast.S
 		return v, true
 	}
 	np = er.b.buildMaxOneRow(np)
-	if len(ExtractCorrelatedCols4LogicalPlan(np)) > 0 {
+	if er.b.disableSubQueryPreprocessing || len(ExtractCorrelatedCols4LogicalPlan(np)) > 0 {
 		er.p = er.b.buildApplyWithJoinType(er.p, np, LeftOuterJoin)
 		if np.Schema().Len() > 1 {
 			newCols := make([]expression.Expression, 0, np.Schema().Len())
diff --git a/planner/core/planbuilder.go b/planner/core/planbuilder.go
index 84954e37575ee..06b94e42bef9c 100644
--- a/planner/core/planbuilder.go
+++ b/planner/core/planbuilder.go
@@ -516,6 +516,8 @@ type PlanBuilder struct {
 	isForUpdateRead             bool
 	allocIDForCTEStorage        int
 	buildingRecursivePartForCTE bool
+	// disableSubQueryPreprocessing indicates whether to pre-process uncorrelated sub-queries in rewriting stage.
+	disableSubQueryPreprocessing bool
 }
 
 type handleColHelper struct {
@@ -617,14 +619,31 @@ func (b *PlanBuilder) popSelectOffset() {
 	b.selectOffset = b.selectOffset[:len(b.selectOffset)-1]
 }
 
+// PlanBuilderOpt is used to adjust the plan builder.
+type PlanBuilderOpt interface {
+	Apply(builder *PlanBuilder)
+}
+
+// PlanBuilderOptNoExecution means the plan builder should not run any executor during Build().
+type PlanBuilderOptNoExecution struct{}
+
+// Apply implements the interface PlanBuilderOpt.
+func (p PlanBuilderOptNoExecution) Apply(builder *PlanBuilder) {
+	builder.disableSubQueryPreprocessing = true
+}
+
 // NewPlanBuilder creates a new PlanBuilder.
-func NewPlanBuilder() *PlanBuilder {
-	return &PlanBuilder{
+func NewPlanBuilder(opts ...PlanBuilderOpt) *PlanBuilder {
+	builder := &PlanBuilder{
 		outerCTEs:           make([]*cteInfo, 0),
 		colMapper:           make(map[*ast.ColumnNameExpr]int),
 		handleHelper:        &handleColHelper{id2HandleMapStack: make([]map[int64][]HandleCols, 0)},
 		correlatedAggMapper: make(map[*ast.AggregateFuncExpr]*expression.CorrelatedColumn),
 	}
+	for _, opt := range opts {
+		opt.Apply(builder)
+	}
+	return builder
 }
 
 // Init initialize a PlanBuilder.