plan: second step of removing parents (pingcap#5451)

plan/explain.go

@@ -21,42 +21,6 @@ import (
 	"github.com/pingcap/tidb/expression/aggregation"
 )
 
-func setParents4FinalPlan(plan PhysicalPlan) {
-	allPlans := []PhysicalPlan{plan}
-	planMark := map[int]bool{}
-	planMark[plan.ID()] = true
-	for pID := 0; pID < len(allPlans); pID++ {
-		allPlans[pID].SetParents()
-		switch copPlan := allPlans[pID].(type) {
-		case *PhysicalTableReader:
-			setParents4FinalPlan(copPlan.tablePlan)
-		case *PhysicalIndexReader:
-			setParents4FinalPlan(copPlan.indexPlan)
-		case *PhysicalIndexLookUpReader:
-			setParents4FinalPlan(copPlan.indexPlan)
-			setParents4FinalPlan(copPlan.tablePlan)
-		}
-		for _, p := range allPlans[pID].Children() {
-			if !planMark[p.ID()] {
-				allPlans = append(allPlans, p.(PhysicalPlan))
-				planMark[p.ID()] = true
-			}
-		}
-	}
-
-	allPlans = allPlans[0:1]
-	planMark[plan.ID()] = false
-	for pID := 0; pID < len(allPlans); pID++ {
-		for _, p := range allPlans[pID].Children() {
-			p.SetParents(allPlans[pID])
-			if planMark[p.ID()] {
-				planMark[p.ID()] = false
-				allPlans = append(allPlans, p.(PhysicalPlan))
-			}
-		}
-	}
-}
-
 // ExplainInfo implements PhysicalPlan interface.
 func (p *PhysicalLock) ExplainInfo() string {
 	return p.Lock.String()

plan/planbuilder.go

@@ -1069,7 +1069,6 @@ func (b *planBuilder) buildExplain(explain *ast.ExplainStmt) Plan {
 			return nil
 		}
 	}
-	setParents4FinalPlan(pp)
 	p := &Explain{StmtPlan: pp}
 	switch strings.ToLower(explain.Format) {
 	case ast.ExplainFormatROW:
@@ -1080,7 +1079,7 @@ func (b *planBuilder) buildExplain(explain *ast.ExplainStmt) Plan {
 		}
 		p.SetSchema(schema)
 		p.explainedPlans = map[int]bool{}
-		p.prepareRootTaskInfo(p.StmtPlan.(PhysicalPlan))
+		p.prepareRootTaskInfo(p.StmtPlan.(PhysicalPlan), "")
 	case ast.ExplainFormatDOT:
 		retFields := []string{"dot contents"}
 		schema := expression.NewSchema(make([]*expression.Column, 0, len(retFields))...)

plan/plans.go

@@ -357,40 +357,38 @@ type Explain struct {
 
 // prepareExplainInfo4DAGTask generates the following information for every plan:
 // ["id", "parents", "task", "operator info"].
-func (e *Explain) prepareExplainInfo4DAGTask(p PhysicalPlan, taskType string) {
-	parents := p.Parents()
-	parentIDs := make([]string, 0, len(parents))
-	for _, parent := range parents {
-		parentIDs = append(parentIDs, parent.ExplainID())
-	}
+func (e *Explain) prepareExplainInfo4DAGTask(p PhysicalPlan, taskType string, parentID string) {
 	childrenIDs := make([]string, 0, len(p.Children()))
 	for _, ch := range p.Children() {
 		childrenIDs = append(childrenIDs, ch.ExplainID())
 	}
-	parentInfo := strings.Join(parentIDs, ",")
 	childrenInfo := strings.Join(childrenIDs, ",")
 	operatorInfo := p.ExplainInfo()
 	count := string(strconv.AppendFloat([]byte{}, p.statsInfo().count, 'f', -1, 64))
-	row := []string{p.ExplainID(), parentInfo, childrenInfo, taskType, operatorInfo, count}
+	row := []string{p.ExplainID(), parentID, childrenInfo, taskType, operatorInfo, count}
 	e.Rows = append(e.Rows, row)
 }
 
 // prepareCopTaskInfo generates explain information for cop-tasks.
 // Only PhysicalTableReader, PhysicalIndexReader and PhysicalIndexLookUpReader have cop-tasks currently.
 func (e *Explain) prepareCopTaskInfo(plans []PhysicalPlan) {
-	for _, p := range plans {
-		e.prepareExplainInfo4DAGTask(p, "cop")
+	for i, p := range plans {
+		var parentID string
+		if i+1 < len(plans) {
+			parentID = plans[i+1].ExplainID()
+		}
+		e.prepareExplainInfo4DAGTask(p, "cop", parentID)
 	}
 }
 
 // prepareRootTaskInfo generates explain information for root-tasks.
-func (e *Explain) prepareRootTaskInfo(p PhysicalPlan) {
+func (e *Explain) prepareRootTaskInfo(p PhysicalPlan, parentID string) {
 	e.explainedPlans[p.ID()] = true
 	for _, child := range p.Children() {
 		if e.explainedPlans[child.ID()] {
 			continue
 		}
-		e.prepareRootTaskInfo(child.(PhysicalPlan))
+		e.prepareRootTaskInfo(child.(PhysicalPlan), p.ExplainID())
 	}
 	switch copPlan := p.(type) {
 	case *PhysicalTableReader:
@@ -401,7 +399,7 @@ func (e *Explain) prepareRootTaskInfo(p PhysicalPlan) {
 		e.prepareCopTaskInfo(copPlan.IndexPlans)
 		e.prepareCopTaskInfo(copPlan.TablePlans)
 	}
-	e.prepareExplainInfo4DAGTask(p, "root")
+	e.prepareExplainInfo4DAGTask(p, "root", parentID)
 }
 
 func (e *Explain) prepareDotInfo(p PhysicalPlan) {