planner: don't DoOptimze when build show (pingcap#12005)

executor/builder.go

@@ -150,7 +150,7 @@ func (b *executorBuilder) build(p plannercore.Plan) Executor {
 		return b.buildShowDDLJobQueries(v)
 	case *plannercore.ShowSlow:
 		return b.buildShowSlow(v)
-	case *plannercore.Show:
+	case *plannercore.PhysicalShow:
 		return b.buildShow(v)
 	case *plannercore.Simple:
 		return b.buildSimple(v)
@@ -604,7 +604,7 @@ func (b *executorBuilder) buildExecute(v *plannercore.Execute) Executor {
 	return e
 }
 
-func (b *executorBuilder) buildShow(v *plannercore.Show) Executor {
+func (b *executorBuilder) buildShow(v *plannercore.PhysicalShow) Executor {
 	e := &ShowExec{
 		baseExecutor: newBaseExecutor(b.ctx, v.Schema(), v.ExplainID()),
 		Tp:           v.Tp,

planner/core/common_plans.go

@@ -22,7 +22,6 @@ import (
 
 	"github.com/pingcap/errors"
 	"github.com/pingcap/parser/ast"
-	"github.com/pingcap/parser/auth"
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/parser/mysql"
 	"github.com/pingcap/tidb/expression"
@@ -367,24 +366,6 @@ type Deallocate struct {
 	Name string
 }
 
-// Show represents a show plan.
-type Show struct {
-	physicalSchemaProducer
-
-	Tp          ast.ShowStmtType // Databases/Tables/Columns/....
-	DBName      string
-	Table       *ast.TableName  // Used for showing columns.
-	Column      *ast.ColumnName // Used for `desc table column`.
-	IndexName   model.CIStr
-	Flag        int                  // Some flag parsed from sql, such as FULL.
-	User        *auth.UserIdentity   // Used for show grants.
-	Roles       []*auth.RoleIdentity // Used for show grants.
-	Full        bool
-	IfNotExists bool // Used for `show create database if not exists`
-
-	GlobalScope bool // Used by show variables
-}
-
 // Set represents a plan for set stmt.
 type Set struct {
 	baseSchemaProducer

planner/core/find_best_task.go

@@ -68,13 +68,21 @@ func (p *LogicalTableDual) findBestTask(prop *property.PhysicalProperty) (task,
 		return invalidTask, nil
 	}
 	dual := PhysicalTableDual{
-		RowCount:    p.RowCount,
-		placeHolder: p.placeHolder,
+		RowCount: p.RowCount,
 	}.Init(p.ctx, p.stats)
 	dual.SetSchema(p.schema)
 	return &rootTask{p: dual}, nil
 }
 
+func (p *LogicalShow) findBestTask(prop *property.PhysicalProperty) (task, error) {
+	if !prop.IsEmpty() {
+		return invalidTask, nil
+	}
+	pShow := PhysicalShow{baseShowContent: p.baseShowContent}.Init(p.ctx)
+	pShow.SetSchema(p.schema)
+	return &rootTask{p: pShow}, nil
+}
+
 // findBestTask implements LogicalPlan interface.
 func (p *baseLogicalPlan) findBestTask(prop *property.PhysicalProperty) (bestTask task, err error) {
 	// If p is an inner plan in an IndexJoin, the IndexJoin will generate an inner plan by itself,

planner/core/initialize.go

@@ -267,8 +267,14 @@ func (p Insert) Init(ctx sessionctx.Context) *Insert {
 	return &p
 }
 
-// Init initializes Show.
-func (p Show) Init(ctx sessionctx.Context) *Show {
+// Init initializes LogicalShow.
+func (p LogicalShow) Init(ctx sessionctx.Context) *LogicalShow {
+	p.baseLogicalPlan = newBaseLogicalPlan(ctx, TypeShow, &p)
+	return &p
+}
+
+// Init initializes PhysicalShow.
+func (p PhysicalShow) Init(ctx sessionctx.Context) *PhysicalShow {
 	p.basePhysicalPlan = newBasePhysicalPlan(ctx, TypeShow, &p)
 	// Just use pseudo stats to avoid panic.
 	p.stats = &property.StatsInfo{RowCount: 1}

planner/core/logical_plan_test.go

@@ -938,7 +938,7 @@ func (s *testPlanSuite) TestPlanBuilder(c *C) {
 		},
 		{
 			sql:  "show columns from t where `Key` = 'pri' like 't*'",
-			plan: "Show->Sel([eq(cast(key), 0)])",
+			plan: "Show->Sel([eq(cast(key), 0)])->Projection",
 		},
 		{
 			sql:  "do sleep(5)",

planner/core/logical_plans.go

@@ -17,6 +17,7 @@ import (
 	"math"
 
 	"github.com/pingcap/parser/ast"
+	"github.com/pingcap/parser/auth"
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/parser/mysql"
 	"github.com/pingcap/tidb/expression"
@@ -316,10 +317,6 @@ type LogicalTableDual struct {
 	logicalSchemaProducer
 
 	RowCount int
-	// placeHolder indicates if this dual plan is a place holder in query optimization
-	// for data sources like `Show`, if true, the dual plan would be substituted by
-	// `Show` in the final plan.
-	placeHolder bool
 }
 
 // LogicalUnionScan is only used in non read-only txn.
@@ -781,3 +778,24 @@ func extractCorColumnsBySchema(p LogicalPlan, schema *expression.Schema) []*expr
 	}
 	return resultCorCols[:length]
 }
+
+type baseShowContent struct {
+	Tp          ast.ShowStmtType // Databases/Tables/Columns/....
+	DBName      string
+	Table       *ast.TableName  // Used for showing columns.
+	Column      *ast.ColumnName // Used for `desc table column`.
+	IndexName   model.CIStr
+	Flag        int                  // Some flag parsed from sql, such as FULL.
+	User        *auth.UserIdentity   // Used for show grants.
+	Roles       []*auth.RoleIdentity // Used for show grants.
+	Full        bool
+	IfNotExists bool // Used for `show create database if not exists`.
+
+	GlobalScope bool // Used by show variables.
+}
+
+// LogicalShow represents a show plan.
+type LogicalShow struct {
+	logicalSchemaProducer
+	baseShowContent
+}

planner/core/physical_plans.go

@@ -407,10 +407,6 @@ type PhysicalTableDual struct {
 	physicalSchemaProducer
 
 	RowCount int
-	// placeHolder indicates if this dual plan is a place holder in query optimization
-	// for data sources like `Show`, if true, the dual plan would be substituted by
-	// `Show` in the final plan.
-	placeHolder bool
 
 	// names is used for OutputNames() method. Dual may be inited when building point get plan.
 	// So it needs to hold names for itself.
@@ -455,6 +451,13 @@ func CollectPlanStatsVersion(plan PhysicalPlan, statsInfos map[string]uint64) ma
 	return statsInfos
 }
 
+// PhysicalShow represents a show plan.
+type PhysicalShow struct {
+	physicalSchemaProducer
+
+	baseShowContent
+}
+
 // BuildMergeJoinPlan builds a PhysicalMergeJoin from the given fields. Currently, it is only used for test purpose.
 func BuildMergeJoinPlan(ctx sessionctx.Context, joinType JoinType, leftKeys, rightKeys []*expression.Column) *PhysicalMergeJoin {
 	baseJoin := basePhysicalJoin{

planner/core/planbuilder.go

@@ -1361,18 +1361,20 @@ func splitWhere(where ast.ExprNode) []ast.ExprNode {
 }
 
 func (b *PlanBuilder) buildShow(ctx context.Context, show *ast.ShowStmt) (Plan, error) {
-	p := Show{
-		Tp:          show.Tp,
-		DBName:      show.DBName,
-		Table:       show.Table,
-		Column:      show.Column,
-		IndexName:   show.IndexName,
-		Flag:        show.Flag,
-		Full:        show.Full,
-		User:        show.User,
-		Roles:       show.Roles,
-		IfNotExists: show.IfNotExists,
-		GlobalScope: show.GlobalScope,
+	p := LogicalShow{
+		baseShowContent: baseShowContent{
+			Tp:          show.Tp,
+			DBName:      show.DBName,
+			Table:       show.Table,
+			Column:      show.Column,
+			IndexName:   show.IndexName,
+			Flag:        show.Flag,
+			Full:        show.Full,
+			User:        show.User,
+			Roles:       show.Roles,
+			IfNotExists: show.IfNotExists,
+			GlobalScope: show.GlobalScope,
+		},
 	}.Init(b.ctx)
 	isView := false
 	switch show.Tp {
@@ -1398,11 +1400,9 @@ func (b *PlanBuilder) buildShow(ctx context.Context, show *ast.ShowStmt) (Plan,
 	for _, col := range p.schema.Columns {
 		col.UniqueID = b.ctx.GetSessionVars().AllocPlanColumnID()
 	}
-	mockTablePlan := LogicalTableDual{placeHolder: true}.Init(b.ctx)
-	mockTablePlan.SetSchema(p.schema)
 	var err error
 	var np LogicalPlan
-	np = mockTablePlan
+	np = p
 	if show.Pattern != nil {
 		show.Pattern.Expr = &ast.ColumnNameExpr{
 			Name: &ast.ColumnName{Name: p.Schema().Columns[0].ColName},
@@ -1418,38 +1418,24 @@ func (b *PlanBuilder) buildShow(ctx context.Context, show *ast.ShowStmt) (Plan,
 			return nil, err
 		}
 	}
-	if np != mockTablePlan {
-		fieldsLen := len(mockTablePlan.schema.Columns)
+	if np != p {
+		b.optFlag |= flagEliminateProjection
+		fieldsLen := len(p.schema.Columns)
 		proj := LogicalProjection{Exprs: make([]expression.Expression, 0, fieldsLen)}.Init(b.ctx)
 		schema := expression.NewSchema(make([]*expression.Column, 0, fieldsLen)...)
-		for _, col := range mockTablePlan.schema.Columns {
+		for _, col := range p.schema.Columns {
 			proj.Exprs = append(proj.Exprs, col)
 			newCol := col.Clone().(*expression.Column)
 			newCol.UniqueID = b.ctx.GetSessionVars().AllocPlanColumnID()
 			schema.Append(newCol)
 		}
 		proj.SetSchema(schema)
 		proj.SetChildren(np)
-		physical, err := DoOptimize(ctx, b.optFlag|flagEliminateProjection, proj)
-		if err != nil {
-			return nil, err
-		}
-		return substitutePlaceHolderDual(physical, p), nil
+		return proj, nil
 	}
 	return p, nil
 }
 
-func substitutePlaceHolderDual(src PhysicalPlan, dst PhysicalPlan) PhysicalPlan {
-	if dual, ok := src.(*PhysicalTableDual); ok && dual.placeHolder {
-		return dst
-	}
-	for i, child := range src.Children() {
-		newChild := substitutePlaceHolderDual(child, dst)
-		src.SetChild(i, newChild)
-	}
-	return src
-}
-
 func (b *PlanBuilder) buildSimple(node ast.StmtNode) (Plan, error) {
 	p := &Simple{Statement: node}
 

planner/core/stats.go

@@ -41,6 +41,20 @@ func (p *LogicalTableDual) DeriveStats(childStats []*property.StatsInfo) (*prope
 	return p.stats, nil
 }
 
+// DeriveStats implement LogicalPlan DeriveStats interface.
+func (p *LogicalShow) DeriveStats(childStats []*property.StatsInfo) (*property.StatsInfo, error) {
+	// A fake count, just to avoid panic now.
+	profile := &property.StatsInfo{
+		RowCount:    1,
+		Cardinality: make([]float64, p.Schema().Len()),
+	}
+	for i := range profile.Cardinality {
+		profile.Cardinality[i] = 1
+	}
+	p.stats = profile
+	return p.stats, nil
+}
+
 func (p *baseLogicalPlan) recursiveDeriveStats() (*property.StatsInfo, error) {
 	if p.stats != nil {
 		return p.stats, nil

planner/core/stringer.go

@@ -113,7 +113,7 @@ func toString(in Plan, strs []string, idxs []int) ([]string, []int) {
 		str = "Lock"
 	case *ShowDDL:
 		str = "ShowDDL"
-	case *Show:
+	case *LogicalShow, *PhysicalShow:
 		str = "Show"
 	case *LogicalSort, *PhysicalSort:
 		str = "Sort"