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gitea/vendor/github.com/pingcap/tidb/executor/explain.go

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// Copyright 2016 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package executor
import (
"strconv"
"strings"
"github.com/pingcap/tidb/ast"
"github.com/pingcap/tidb/optimizer/plan"
"github.com/pingcap/tidb/parser/opcode"
"github.com/pingcap/tidb/util/types"
)
type explainEntry struct {
ID int64
selectType string
table string
joinType string
possibleKeys string
key string
keyLen string
ref string
rows int64
extra []string
}
func (e *explainEntry) setJoinTypeForTableScan(p *plan.TableScan) {
if len(p.AccessConditions) == 0 {
e.joinType = "ALL"
return
}
if p.RefAccess {
e.joinType = "eq_ref"
return
}
for _, con := range p.AccessConditions {
if x, ok := con.(*ast.BinaryOperationExpr); ok {
if x.Op == opcode.EQ {
e.joinType = "const"
return
}
}
}
e.joinType = "range"
}
func (e *explainEntry) setJoinTypeForIndexScan(p *plan.IndexScan) {
if len(p.AccessConditions) == 0 {
e.joinType = "index"
return
}
if len(p.AccessConditions) == p.AccessEqualCount {
if p.RefAccess {
if p.Index.Unique {
e.joinType = "eq_ref"
} else {
e.joinType = "ref"
}
} else {
if p.Index.Unique {
e.joinType = "const"
} else {
e.joinType = "range"
}
}
return
}
e.joinType = "range"
}
// ExplainExec represents an explain executor.
// See: https://dev.mysql.com/doc/refman/5.7/en/explain-output.html
type ExplainExec struct {
StmtPlan plan.Plan
fields []*ast.ResultField
rows []*Row
cursor int
}
// Fields implements Executor Fields interface.
func (e *ExplainExec) Fields() []*ast.ResultField {
return e.fields
}
// Next implements Execution Next interface.
func (e *ExplainExec) Next() (*Row, error) {
if e.rows == nil {
e.fetchRows()
}
if e.cursor >= len(e.rows) {
return nil, nil
}
row := e.rows[e.cursor]
e.cursor++
return row, nil
}
func (e *ExplainExec) fetchRows() {
visitor := &explainVisitor{id: 1}
e.StmtPlan.Accept(visitor)
for _, entry := range visitor.entries {
row := &Row{}
row.Data = types.MakeDatums(
entry.ID,
entry.selectType,
entry.table,
entry.joinType,
entry.key,
entry.key,
entry.keyLen,
entry.ref,
entry.rows,
strings.Join(entry.extra, "; "),
)
for i := range row.Data {
if row.Data[i].Kind() == types.KindString && row.Data[i].GetString() == "" {
row.Data[i].SetNull()
}
}
e.rows = append(e.rows, row)
}
}
// Close implements Executor Close interface.
func (e *ExplainExec) Close() error {
return nil
}
type explainVisitor struct {
id int64
// Sort extra should be appended in the first table in a join.
sort bool
entries []*explainEntry
}
func (v *explainVisitor) Enter(p plan.Plan) (plan.Plan, bool) {
switch x := p.(type) {
case *plan.TableScan:
v.entries = append(v.entries, v.newEntryForTableScan(x))
case *plan.IndexScan:
v.entries = append(v.entries, v.newEntryForIndexScan(x))
case *plan.Sort:
v.sort = true
}
return p, false
}
func (v *explainVisitor) Leave(p plan.Plan) (plan.Plan, bool) {
return p, true
}
func (v *explainVisitor) newEntryForTableScan(p *plan.TableScan) *explainEntry {
entry := &explainEntry{
ID: v.id,
selectType: "SIMPLE",
table: p.Table.Name.O,
}
entry.setJoinTypeForTableScan(p)
if entry.joinType != "ALL" {
entry.key = "PRIMARY"
entry.keyLen = "8"
}
if len(p.AccessConditions)+len(p.FilterConditions) > 0 {
entry.extra = append(entry.extra, "Using where")
}
v.setSortExtra(entry)
return entry
}
func (v *explainVisitor) newEntryForIndexScan(p *plan.IndexScan) *explainEntry {
entry := &explainEntry{
ID: v.id,
selectType: "SIMPLE",
table: p.Table.Name.O,
key: p.Index.Name.O,
}
if len(p.AccessConditions) != 0 {
keyLen := 0
for i := 0; i < len(p.Index.Columns); i++ {
if i < p.AccessEqualCount {
keyLen += p.Index.Columns[i].Length
} else if i < len(p.AccessConditions) {
keyLen += p.Index.Columns[i].Length
break
}
}
entry.keyLen = strconv.Itoa(keyLen)
}
entry.setJoinTypeForIndexScan(p)
if len(p.AccessConditions)+len(p.FilterConditions) > 0 {
entry.extra = append(entry.extra, "Using where")
}
v.setSortExtra(entry)
return entry
}
func (v *explainVisitor) setSortExtra(entry *explainEntry) {
if v.sort {
entry.extra = append(entry.extra, "Using filesort")
v.sort = false
}
}