tidb rule_topn_push_down 源码
tidb rule_topn_push_down 代码
文件路径：/planner/core/rule_topn_push_down.go
// Copyright 2017 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package core
import (
"bytes"
"context"
"fmt"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/planner/util"
"github.com/pingcap/tidb/util/mathutil"
)
// pushDownTopNOptimizer pushes down the topN or limit. In the future we will remove the limit from `requiredProperty` in CBO phase.
type pushDownTopNOptimizer struct {
}
func (s *pushDownTopNOptimizer) optimize(_ context.Context, p LogicalPlan, opt *logicalOptimizeOp) (LogicalPlan, error) {
return p.pushDownTopN(nil, opt), nil
}
func (s *baseLogicalPlan) pushDownTopN(topN *LogicalTopN, opt *logicalOptimizeOp) LogicalPlan {
p := s.self
for i, child := range p.Children() {
p.Children()[i] = child.pushDownTopN(nil, opt)
}
if topN != nil {
return topN.setChild(p, opt)
}
return p
}
// setChild set p as topn's child.
func (lt *LogicalTopN) setChild(p LogicalPlan, opt *logicalOptimizeOp) LogicalPlan {
// Remove this TopN if its child is a TableDual.
dual, isDual := p.(*LogicalTableDual)
if isDual {
numDualRows := uint64(dual.RowCount)
if numDualRows < lt.Offset {
dual.RowCount = 0
return dual
}
dual.RowCount = int(mathutil.Min(numDualRows-lt.Offset, lt.Count))
return dual
}
if lt.isLimit() {
limit := LogicalLimit{
Count: lt.Count,
Offset: lt.Offset,
limitHints: lt.limitHints,
}.Init(lt.ctx, lt.blockOffset)
limit.SetChildren(p)
appendTopNPushDownTraceStep(limit, p, opt)
return limit
}
// Then lt must be topN.
lt.SetChildren(p)
appendTopNPushDownTraceStep(lt, p, opt)
return lt
}
func (ls *LogicalSort) pushDownTopN(topN *LogicalTopN, opt *logicalOptimizeOp) LogicalPlan {
if topN == nil {
return ls.baseLogicalPlan.pushDownTopN(nil, opt)
} else if topN.isLimit() {
topN.ByItems = ls.ByItems
appendSortPassByItemsTraceStep(ls, topN, opt)
return ls.children[0].pushDownTopN(topN, opt)
}
// If a TopN is pushed down, this sort is useless.
return ls.children[0].pushDownTopN(topN, opt)
}
func (p *LogicalLimit) convertToTopN(opt *logicalOptimizeOp) *LogicalTopN {
topn := LogicalTopN{Offset: p.Offset, Count: p.Count, limitHints: p.limitHints}.Init(p.ctx, p.blockOffset)
appendConvertTopNTraceStep(p, topn, opt)
return topn
}
func (p *LogicalLimit) pushDownTopN(topN *LogicalTopN, opt *logicalOptimizeOp) LogicalPlan {
child := p.children[0].pushDownTopN(p.convertToTopN(opt), opt)
if topN != nil {
return topN.setChild(child, opt)
}
return child
}
func (p *LogicalUnionAll) pushDownTopN(topN *LogicalTopN, opt *logicalOptimizeOp) LogicalPlan {
for i, child := range p.children {
var newTopN *LogicalTopN
if topN != nil {
newTopN = LogicalTopN{Count: topN.Count + topN.Offset, limitHints: topN.limitHints}.Init(p.ctx, topN.blockOffset)
for _, by := range topN.ByItems {
newTopN.ByItems = append(newTopN.ByItems, &util.ByItems{Expr: by.Expr, Desc: by.Desc})
}
// newTopN to push down Union's child
appendNewTopNTraceStep(topN, p, opt)
}
p.children[i] = child.pushDownTopN(newTopN, opt)
}
if topN != nil {
return topN.setChild(p, opt)
}
return p
}
func (p *LogicalProjection) pushDownTopN(topN *LogicalTopN, opt *logicalOptimizeOp) LogicalPlan {
for _, expr := range p.Exprs {
if expression.HasAssignSetVarFunc(expr) {
return p.baseLogicalPlan.pushDownTopN(topN, opt)
}
}
if topN != nil {
for _, by := range topN.ByItems {
by.Expr = expression.FoldConstant(expression.ColumnSubstitute(by.Expr, p.schema, p.Exprs))
}
// remove meaningless constant sort items.
for i := len(topN.ByItems) - 1; i >= 0; i-- {
switch topN.ByItems[i].Expr.(type) {
case *expression.Constant, *expression.CorrelatedColumn:
topN.ByItems = append(topN.ByItems[:i], topN.ByItems[i+1:]...)
}
}
}
p.children[0] = p.children[0].pushDownTopN(topN, opt)
return p
}
func (p *LogicalLock) pushDownTopN(topN *LogicalTopN, opt *logicalOptimizeOp) LogicalPlan {
if topN != nil {
p.children[0] = p.children[0].pushDownTopN(topN, opt)
}
return p.self
}
// pushDownTopNToChild will push a topN to one child of join. The idx stands for join child index. 0 is for left child.
func (p *LogicalJoin) pushDownTopNToChild(topN *LogicalTopN, idx int, opt *logicalOptimizeOp) LogicalPlan {
if topN == nil {
return p.children[idx].pushDownTopN(nil, opt)
}
for _, by := range topN.ByItems {
cols := expression.ExtractColumns(by.Expr)
for _, col := range cols {
if !p.children[idx].Schema().Contains(col) {
return p.children[idx].pushDownTopN(nil, opt)
}
}
}
newTopN := LogicalTopN{
Count: topN.Count + topN.Offset,
ByItems: make([]*util.ByItems, len(topN.ByItems)),
limitHints: topN.limitHints,
}.Init(topN.ctx, topN.blockOffset)
for i := range topN.ByItems {
newTopN.ByItems[i] = topN.ByItems[i].Clone()
}
appendTopNPushDownJoinTraceStep(p, newTopN, idx, opt)
return p.children[idx].pushDownTopN(newTopN, opt)
}
func (p *LogicalJoin) pushDownTopN(topN *LogicalTopN, opt *logicalOptimizeOp) LogicalPlan {
switch p.JoinType {
case LeftOuterJoin, LeftOuterSemiJoin, AntiLeftOuterSemiJoin:
p.children[0] = p.pushDownTopNToChild(topN, 0, opt)
p.children[1] = p.children[1].pushDownTopN(nil, opt)
case RightOuterJoin:
p.children[1] = p.pushDownTopNToChild(topN, 1, opt)
p.children[0] = p.children[0].pushDownTopN(nil, opt)
default:
return p.baseLogicalPlan.pushDownTopN(topN, opt)
}
// The LogicalJoin may be also a LogicalApply. So we must use self to set parents.
if topN != nil {
return topN.setChild(p.self, opt)
}
return p.self
}
func (*pushDownTopNOptimizer) name() string {
return "topn_push_down"
}
func appendTopNPushDownTraceStep(parent LogicalPlan, child LogicalPlan, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v is added as %v_%v's parent", parent.TP(), parent.ID(), child.TP(), child.ID())
}
reason := func() string {
return fmt.Sprintf("%v is pushed down", parent.TP())
}
opt.appendStepToCurrent(parent.ID(), parent.TP(), reason, action)
}
func appendTopNPushDownJoinTraceStep(p *LogicalJoin, topN *LogicalTopN, idx int, opt *logicalOptimizeOp) {
action := func() string {
buffer := bytes.NewBufferString(fmt.Sprintf("%v_%v is added and pushed into %v_%v's ",
topN.TP(), topN.ID(), p.TP(), p.ID()))
if idx == 0 {
buffer.WriteString("left ")
} else {
buffer.WriteString("right ")
}
buffer.WriteString("table")
return buffer.String()
}
reason := func() string {
buffer := bytes.NewBufferString(fmt.Sprintf("%v_%v's joinType is %v, and all ByItems[", p.TP(), p.ID(), p.JoinType.String()))
for i, item := range topN.ByItems {
if i > 0 {
buffer.WriteString(",")
}
buffer.WriteString(item.String())
}
buffer.WriteString("] contained in ")
if idx == 0 {
buffer.WriteString("left ")
} else {
buffer.WriteString("right ")
}
buffer.WriteString("table")
return buffer.String()
}
opt.appendStepToCurrent(p.ID(), p.TP(), reason, action)
}
func appendSortPassByItemsTraceStep(sort *LogicalSort, topN *LogicalTopN, opt *logicalOptimizeOp) {
action := func() string {
buffer := bytes.NewBufferString(fmt.Sprintf("%v_%v passes ByItems[", sort.TP(), sort.ID()))
for i, item := range sort.ByItems {
if i > 0 {
buffer.WriteString(",")
}
buffer.WriteString(item.String())
}
buffer.WriteString(fmt.Sprintf("] to %v_%v", topN.TP(), topN.ID()))
return buffer.String()
}
reason := func() string {
return fmt.Sprintf("%v_%v is Limit originally", topN.TP(), topN.ID())
}
opt.appendStepToCurrent(sort.ID(), sort.TP(), reason, action)
}
func appendNewTopNTraceStep(topN *LogicalTopN, union *LogicalUnionAll, opt *logicalOptimizeOp) {
reason := func() string {
return ""
}
action := func() string {
return fmt.Sprintf("%v_%v is added and pushed down across %v_%v", topN.TP(), topN.ID(), union.TP(), union.ID())
}
opt.appendStepToCurrent(topN.ID(), topN.TP(), reason, action)
}
func appendConvertTopNTraceStep(p LogicalPlan, topN *LogicalTopN, opt *logicalOptimizeOp) {
reason := func() string {
return ""
}
action := func() string {
return fmt.Sprintf("%v_%v is converted into %v_%v", p.TP(), p.ID(), topN.TP(), topN.ID())
}
opt.appendStepToCurrent(topN.ID(), topN.TP(), reason, action)
}
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