executor: support Chunk for ExplainExec (pingcap#5398)

executor/builder.go

@@ -424,14 +424,15 @@ func (b *executorBuilder) buildDDL(v *plan.DDL) Executor {
 }
 
 func (b *executorBuilder) buildExplain(v *plan.Explain) Executor {
-	exec := &ExplainExec{
+	e := &ExplainExec{
 		baseExecutor: newBaseExecutor(v.Schema(), b.ctx),
 	}
-	exec.rows = make([]Row, 0, len(v.Rows))
+	e.rows = make([][]string, 0, len(v.Rows))
 	for _, row := range v.Rows {
-		exec.rows = append(exec.rows, row)
+		e.rows = append(e.rows, row)
 	}
-	return exec
+	e.supportChk = true
+	return e
 }
 
 func (b *executorBuilder) buildUnionScanExec(v *plan.PhysicalUnionScan) Executor {

executor/explain.go

@@ -13,13 +13,18 @@
 
 package executor
 
-import goctx "golang.org/x/net/context"
+import (
+	"github.com/cznic/mathutil"
+	"github.com/pingcap/tidb/types"
+	"github.com/pingcap/tidb/util/chunk"
+	goctx "golang.org/x/net/context"
+)
 
 // ExplainExec represents an explain executor.
 type ExplainExec struct {
 	baseExecutor
 
-	rows   []Row
+	rows   [][]string
 	cursor int
 }
 
@@ -28,13 +33,33 @@ func (e *ExplainExec) Next(goCtx goctx.Context) (Row, error) {
 	if e.cursor >= len(e.rows) {
 		return nil, nil
 	}
-	row := e.rows[e.cursor]
+	resultRow := make([]types.Datum, 0, len(e.rows[0]))
+	for i := range e.rows[e.cursor] {
+		resultRow = append(resultRow, types.NewStringDatum(e.rows[e.cursor][i]))
+	}
 	e.cursor++
-	return row, nil
+	return resultRow, nil
 }
 
 // Close implements the Executor Close interface.
 func (e *ExplainExec) Close() error {
 	e.rows = nil
 	return nil
 }
+
+// NextChunk implements the Executor NextChunk interface.
+func (e *ExplainExec) NextChunk(goCtx goctx.Context, chk *chunk.Chunk) error {
+	chk.Reset()
+	if e.cursor >= len(e.rows) {
+		return nil
+	}
+
+	numCurRows := mathutil.Min(e.ctx.GetSessionVars().MaxChunkSize, len(e.rows)-e.cursor)
+	for i := e.cursor; i < e.cursor+numCurRows; i++ {
+		for j := range e.rows[i] {
+			chk.AppendString(j, e.rows[i][j])
+		}
+	}
+	e.cursor += numCurRows
+	return nil
+}

plan/planbuilder.go

@@ -1058,12 +1058,11 @@ func (b *planBuilder) buildExplain(explain *ast.ExplainStmt) Plan {
 	p := &Explain{StmtPlan: pp}
 	switch strings.ToLower(explain.Format) {
 	case ast.ExplainFormatROW:
-		retFields := []string{"id", "parents", "children", "task", "operator info"}
+		retFields := []string{"id", "parents", "children", "task", "operator info", "count"}
 		schema := expression.NewSchema(make([]*expression.Column, 0, len(retFields))...)
 		for _, fieldName := range retFields {
 			schema.Append(buildColumn("", fieldName, mysql.TypeString, mysql.MaxBlobWidth))
 		}
-		schema.Append(buildColumn("", "count", mysql.TypeDouble, mysql.MaxRealWidth))
 		p.SetSchema(schema)
 		p.explainedPlans = map[int]bool{}
 		p.prepareRootTaskInfo(p.StmtPlan.(PhysicalPlan))

plan/plans.go

@@ -15,8 +15,8 @@ package plan
 
 import (
 	"bytes"
-	"encoding/json"
 	"fmt"
+	"strconv"
 	"strings"
 
 	"github.com/juju/errors"
@@ -27,7 +27,6 @@ import (
 	"github.com/pingcap/tidb/model"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/table"
-	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/auth"
 	"github.com/pingcap/tidb/util/kvcache"
 )
@@ -284,30 +283,10 @@ type Explain struct {
 	basePlan
 
 	StmtPlan       Plan
-	Rows           [][]types.Datum
+	Rows           [][]string
 	explainedPlans map[int]bool
 }
 
-func (e *Explain) prepareExplainInfo(p Plan, parent Plan) error {
-	for _, child := range p.Children() {
-		err := e.prepareExplainInfo(child, p)
-		if err != nil {
-			return errors.Trace(err)
-		}
-	}
-	explain, err := json.MarshalIndent(p, "", "    ")
-	if err != nil {
-		return errors.Trace(err)
-	}
-	parentStr := ""
-	if parent != nil {
-		parentStr = parent.ExplainID()
-	}
-	row := types.MakeDatums(p.ExplainID(), string(explain), parentStr)
-	e.Rows = append(e.Rows, row)
-	return nil
-}
-
 // prepareExplainInfo4DAGTask generates the following information for every plan:
 // ["id", "parents", "task", "operator info"].
 func (e *Explain) prepareExplainInfo4DAGTask(p PhysicalPlan, taskType string) {
@@ -323,8 +302,8 @@ func (e *Explain) prepareExplainInfo4DAGTask(p PhysicalPlan, taskType string) {
 	parentInfo := strings.Join(parentIDs, ",")
 	childrenInfo := strings.Join(childrenIDs, ",")
 	operatorInfo := p.ExplainInfo()
-	count := p.statsProfile().count
-	row := types.MakeDatums(p.ExplainID(), parentInfo, childrenInfo, taskType, operatorInfo, count)
+	count := string(strconv.AppendFloat([]byte{}, p.statsProfile().count, 'f', -1, 64))
+	row := []string{p.ExplainID(), parentInfo, childrenInfo, taskType, operatorInfo, count}
 	e.Rows = append(e.Rows, row)
 }
 
@@ -363,8 +342,7 @@ func (e *Explain) prepareDotInfo(p PhysicalPlan) {
 	e.prepareTaskDot(p, "root", buffer)
 	buffer.WriteString(fmt.Sprintln("}"))
 
-	row := types.MakeDatums(buffer.String())
-	e.Rows = append(e.Rows, row)
+	e.Rows = append(e.Rows, []string{buffer.String()})
 }
 
 func (e *Explain) prepareTaskDot(p PhysicalPlan, taskTp string, buffer *bytes.Buffer) {