tidb rule_decorrelate 源码
tidb rule_decorrelate 代码
文件路径：/planner/core/rule_decorrelate.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"
"math"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/expression/aggregation"
"github.com/pingcap/tidb/parser/ast"
"github.com/pingcap/tidb/parser/mysql"
"github.com/pingcap/tidb/types"
"github.com/pingcap/tidb/util/plancodec"
)
// canPullUpAgg checks if an apply can pull an aggregation up.
func (la *LogicalApply) canPullUpAgg() bool {
if la.JoinType != InnerJoin && la.JoinType != LeftOuterJoin {
return false
}
if len(la.EqualConditions)+len(la.LeftConditions)+len(la.RightConditions)+len(la.OtherConditions) > 0 {
return false
}
return len(la.children[0].Schema().Keys) > 0
}
// canPullUp checks if an aggregation can be pulled up. An aggregate function like count(*) cannot be pulled up.
func (la *LogicalAggregation) canPullUp() bool {
if len(la.GroupByItems) > 0 {
return false
}
for _, f := range la.AggFuncs {
for _, arg := range f.Args {
expr := expression.EvaluateExprWithNull(la.ctx, la.children[0].Schema(), arg)
if con, ok := expr.(*expression.Constant); !ok || !con.Value.IsNull() {
return false
}
}
}
return true
}
// deCorColFromEqExpr checks whether it's an equal condition of form `col = correlated col`. If so we will change the decorrelated
// column to normal column to make a new equal condition.
func (la *LogicalApply) deCorColFromEqExpr(expr expression.Expression) expression.Expression {
sf, ok := expr.(*expression.ScalarFunction)
if !ok || sf.FuncName.L != ast.EQ {
return nil
}
if col, lOk := sf.GetArgs()[0].(*expression.Column); lOk {
if corCol, rOk := sf.GetArgs()[1].(*expression.CorrelatedColumn); rOk {
ret := corCol.Decorrelate(la.Schema())
if _, ok := ret.(*expression.CorrelatedColumn); ok {
return nil
}
// We should make sure that the equal condition's left side is the join's left join key, right is the right key.
return expression.NewFunctionInternal(la.ctx, ast.EQ, types.NewFieldType(mysql.TypeTiny), ret, col)
}
}
if corCol, lOk := sf.GetArgs()[0].(*expression.CorrelatedColumn); lOk {
if col, rOk := sf.GetArgs()[1].(*expression.Column); rOk {
ret := corCol.Decorrelate(la.Schema())
if _, ok := ret.(*expression.CorrelatedColumn); ok {
return nil
}
// We should make sure that the equal condition's left side is the join's left join key, right is the right key.
return expression.NewFunctionInternal(la.ctx, ast.EQ, types.NewFieldType(mysql.TypeTiny), ret, col)
}
}
return nil
}
// ExtractCorrelatedCols4LogicalPlan recursively extracts all of the correlated columns
// from a plan tree by calling LogicalPlan.ExtractCorrelatedCols.
func ExtractCorrelatedCols4LogicalPlan(p LogicalPlan) []*expression.CorrelatedColumn {
corCols := p.ExtractCorrelatedCols()
for _, child := range p.Children() {
corCols = append(corCols, ExtractCorrelatedCols4LogicalPlan(child)...)
}
return corCols
}
// ExtractCorrelatedCols4PhysicalPlan recursively extracts all of the correlated columns
// from a plan tree by calling PhysicalPlan.ExtractCorrelatedCols.
func ExtractCorrelatedCols4PhysicalPlan(p PhysicalPlan) []*expression.CorrelatedColumn {
corCols := p.ExtractCorrelatedCols()
for _, child := range p.Children() {
corCols = append(corCols, ExtractCorrelatedCols4PhysicalPlan(child)...)
}
return corCols
}
// decorrelateSolver tries to convert apply plan to join plan.
type decorrelateSolver struct{}
func (s *decorrelateSolver) aggDefaultValueMap(agg *LogicalAggregation) map[int]*expression.Constant {
defaultValueMap := make(map[int]*expression.Constant, len(agg.AggFuncs))
for i, f := range agg.AggFuncs {
switch f.Name {
case ast.AggFuncBitOr, ast.AggFuncBitXor, ast.AggFuncCount:
defaultValueMap[i] = expression.NewZero()
case ast.AggFuncBitAnd:
defaultValueMap[i] = &expression.Constant{Value: types.NewUintDatum(math.MaxUint64), RetType: types.NewFieldType(mysql.TypeLonglong)}
}
}
return defaultValueMap
}
// optimize implements logicalOptRule interface.
func (s *decorrelateSolver) optimize(ctx context.Context, p LogicalPlan, opt *logicalOptimizeOp) (LogicalPlan, error) {
if apply, ok := p.(*LogicalApply); ok {
outerPlan := apply.children[0]
innerPlan := apply.children[1]
apply.CorCols = extractCorColumnsBySchema4LogicalPlan(apply.children[1], apply.children[0].Schema())
if len(apply.CorCols) == 0 {
// If the inner plan is non-correlated, the apply will be simplified to join.
join := &apply.LogicalJoin
join.self = join
join.tp = plancodec.TypeJoin
p = join
appendApplySimplifiedTraceStep(apply, join, opt)
} else if sel, ok := innerPlan.(*LogicalSelection); ok {
// If the inner plan is a selection, we add this condition to join predicates.
// Notice that no matter what kind of join is, it's always right.
newConds := make([]expression.Expression, 0, len(sel.Conditions))
for _, cond := range sel.Conditions {
newConds = append(newConds, cond.Decorrelate(outerPlan.Schema()))
}
apply.AttachOnConds(newConds)
innerPlan = sel.children[0]
apply.SetChildren(outerPlan, innerPlan)
appendRemoveSelectionTraceStep(apply, sel, opt)
return s.optimize(ctx, p, opt)
} else if m, ok := innerPlan.(*LogicalMaxOneRow); ok {
if m.children[0].MaxOneRow() {
innerPlan = m.children[0]
apply.SetChildren(outerPlan, innerPlan)
appendRemoveMaxOneRowTraceStep(m, opt)
return s.optimize(ctx, p, opt)
}
} else if proj, ok := innerPlan.(*LogicalProjection); ok {
// After the column pruning, some expressions in the projection operator may be pruned.
// In this situation, we can decorrelate the apply operator.
allConst := len(proj.Exprs) > 0
for _, expr := range proj.Exprs {
if len(expression.ExtractCorColumns(expr)) > 0 || !expression.ExtractColumnSet(expr).IsEmpty() {
allConst = false
break
}
}
if allConst && apply.JoinType == LeftOuterJoin {
// If the projection just references some constant. We cannot directly pull it up when the APPLY is an outer join.
// e.g. select (select 1 from t1 where t1.a=t2.a) from t2; When the t1.a=t2.a is false the join's output is NULL.
// But if we pull the projection upon the APPLY. It will return 1 since the projection is evaluated after the join.
// We disable the decorrelation directly for now.
// TODO: Actually, it can be optimized. We need to first push the projection down to the selection. And then the APPLY can be decorrelated.
goto NoOptimize
}
// step1: substitute the all the schema with new expressions (including correlated column maybe, but it doesn't affect the collation infer inside)
// eg: projection: constant("guo") --> column8, once upper layer substitution failed here, the lower layer behind
// projection can't supply column8 anymore.
//
// upper OP (depend on column8) --> projection(constant "guo" --> column8) --> lower layer OP
// | ^
// +-------------------------------------------------------+
//
// upper OP (depend on column8) --> lower layer OP
// | ^
// +-----------------------------+ // Fail: lower layer can't supply column8 anymore.
hasFail := apply.columnSubstituteAll(proj.Schema(), proj.Exprs)
if hasFail {
goto NoOptimize
}
// step2: when it can be substituted all, we then just do the de-correlation (apply conditions included).
for i, expr := range proj.Exprs {
proj.Exprs[i] = expr.Decorrelate(outerPlan.Schema())
}
apply.decorrelate(outerPlan.Schema())
innerPlan = proj.children[0]
apply.SetChildren(outerPlan, innerPlan)
if apply.JoinType != SemiJoin && apply.JoinType != LeftOuterSemiJoin && apply.JoinType != AntiSemiJoin && apply.JoinType != AntiLeftOuterSemiJoin {
proj.SetSchema(apply.Schema())
proj.Exprs = append(expression.Column2Exprs(outerPlan.Schema().Clone().Columns), proj.Exprs...)
apply.SetSchema(expression.MergeSchema(outerPlan.Schema(), innerPlan.Schema()))
np, err := s.optimize(ctx, p, opt)
if err != nil {
return nil, err
}
proj.SetChildren(np)
appendMoveProjTraceStep(apply, np, proj, opt)
return proj, nil
}
appendRemoveProjTraceStep(apply, proj, opt)
return s.optimize(ctx, p, opt)
} else if li, ok := innerPlan.(*LogicalLimit); ok {
// The presence of 'limit' in 'exists' will make the plan not optimal, so we need to decorrelate the 'limit' of subquery in optimization.
// e.g. select count(*) from test t1 where exists (select value from test t2 where t1.id = t2.id limit 1); When using 'limit' in subquery, the plan will not optimal.
// If apply is not SemiJoin, the output of it might be expanded even though we are `limit 1`.
if apply.JoinType != SemiJoin && apply.JoinType != LeftOuterSemiJoin && apply.JoinType != AntiSemiJoin && apply.JoinType != AntiLeftOuterSemiJoin {
goto NoOptimize
}
// If subquery has some filter condition, we will not optimize limit.
if len(apply.LeftConditions) > 0 || len(apply.RightConditions) > 0 || len(apply.OtherConditions) > 0 || len(apply.EqualConditions) > 0 {
goto NoOptimize
}
// Limit with non-0 offset will conduct an impact of itself on the final result set from its sub-child, consequently determining the bool value of the exist subquery.
if li.Offset == 0 {
innerPlan = li.children[0]
apply.SetChildren(outerPlan, innerPlan)
appendRemoveLimitTraceStep(li, opt)
return s.optimize(ctx, p, opt)
}
} else if agg, ok := innerPlan.(*LogicalAggregation); ok {
if apply.canPullUpAgg() && agg.canPullUp() {
innerPlan = agg.children[0]
apply.JoinType = LeftOuterJoin
apply.SetChildren(outerPlan, innerPlan)
agg.SetSchema(apply.Schema())
agg.GroupByItems = expression.Column2Exprs(outerPlan.Schema().Keys[0])
newAggFuncs := make([]*aggregation.AggFuncDesc, 0, apply.Schema().Len())
outerColsInSchema := make([]*expression.Column, 0, outerPlan.Schema().Len())
for i, col := range outerPlan.Schema().Columns {
first, err := aggregation.NewAggFuncDesc(agg.ctx, ast.AggFuncFirstRow, []expression.Expression{col}, false)
if err != nil {
return nil, err
}
newAggFuncs = append(newAggFuncs, first)
outerCol, _ := outerPlan.Schema().Columns[i].Clone().(*expression.Column)
outerCol.RetType = first.RetTp
outerColsInSchema = append(outerColsInSchema, outerCol)
}
apply.SetSchema(expression.MergeSchema(expression.NewSchema(outerColsInSchema...), innerPlan.Schema()))
resetNotNullFlag(apply.schema, outerPlan.Schema().Len(), apply.schema.Len())
for i, aggFunc := range agg.AggFuncs {
aggArgs := make([]expression.Expression, 0, len(aggFunc.Args))
for _, arg := range aggFunc.Args {
switch expr := arg.(type) {
case *expression.Column:
if idx := apply.schema.ColumnIndex(expr); idx != -1 {
aggArgs = append(aggArgs, apply.schema.Columns[idx])
} else {
aggArgs = append(aggArgs, expr)
}
case *expression.ScalarFunction:
expr.RetType = expr.RetType.Clone()
expr.RetType.DelFlag(mysql.NotNullFlag)
aggArgs = append(aggArgs, expr)
default:
aggArgs = append(aggArgs, expr)
}
}
desc, err := aggregation.NewAggFuncDesc(agg.ctx, agg.AggFuncs[i].Name, aggArgs, agg.AggFuncs[i].HasDistinct)
if err != nil {
return nil, err
}
newAggFuncs = append(newAggFuncs, desc)
}
agg.AggFuncs = newAggFuncs
np, err := s.optimize(ctx, p, opt)
if err != nil {
return nil, err
}
agg.SetChildren(np)
appendPullUpAggTraceStep(apply, np, agg, opt)
// TODO: Add a Projection if any argument of aggregate funcs or group by items are scalar functions.
// agg.buildProjectionIfNecessary()
return agg, nil
}
// We can pull up the equal conditions below the aggregation as the join key of the apply, if only
// the equal conditions contain the correlated column of this apply.
if sel, ok := agg.children[0].(*LogicalSelection); ok && apply.JoinType == LeftOuterJoin {
var (
eqCondWithCorCol []*expression.ScalarFunction
remainedExpr []expression.Expression
)
// Extract the equal condition.
for _, cond := range sel.Conditions {
if expr := apply.deCorColFromEqExpr(cond); expr != nil {
eqCondWithCorCol = append(eqCondWithCorCol, expr.(*expression.ScalarFunction))
} else {
remainedExpr = append(remainedExpr, cond)
}
}
if len(eqCondWithCorCol) > 0 {
originalExpr := sel.Conditions
sel.Conditions = remainedExpr
apply.CorCols = extractCorColumnsBySchema4LogicalPlan(apply.children[1], apply.children[0].Schema())
// There's no other correlated column.
groupByCols := expression.NewSchema(agg.GetGroupByCols()...)
if len(apply.CorCols) == 0 {
appendedGroupByCols := expression.NewSchema()
var appendedAggFuncs []*aggregation.AggFuncDesc
join := &apply.LogicalJoin
join.EqualConditions = append(join.EqualConditions, eqCondWithCorCol...)
for _, eqCond := range eqCondWithCorCol {
clonedCol := eqCond.GetArgs()[1].(*expression.Column)
// If the join key is not in the aggregation's schema, add first row function.
if agg.schema.ColumnIndex(eqCond.GetArgs()[1].(*expression.Column)) == -1 {
newFunc, err := aggregation.NewAggFuncDesc(apply.ctx, ast.AggFuncFirstRow, []expression.Expression{clonedCol}, false)
if err != nil {
return nil, err
}
agg.AggFuncs = append(agg.AggFuncs, newFunc)
agg.schema.Append(clonedCol)
agg.schema.Columns[agg.schema.Len()-1].RetType = newFunc.RetTp
appendedAggFuncs = append(appendedAggFuncs, newFunc)
}
// If group by cols don't contain the join key, add it into this.
if !groupByCols.Contains(clonedCol) {
agg.GroupByItems = append(agg.GroupByItems, clonedCol)
groupByCols.Append(clonedCol)
appendedGroupByCols.Append(clonedCol)
}
}
// The selection may be useless, check and remove it.
if len(sel.Conditions) == 0 {
agg.SetChildren(sel.children[0])
appendRemoveSelectionTraceStep(agg, sel, opt)
}
defaultValueMap := s.aggDefaultValueMap(agg)
// We should use it directly, rather than building a projection.
if len(defaultValueMap) > 0 {
proj := LogicalProjection{}.Init(agg.ctx, agg.blockOffset)
proj.SetSchema(apply.schema)
proj.Exprs = expression.Column2Exprs(apply.schema.Columns)
for i, val := range defaultValueMap {
pos := proj.schema.ColumnIndex(agg.schema.Columns[i])
ifNullFunc := expression.NewFunctionInternal(agg.ctx, ast.Ifnull, types.NewFieldType(mysql.TypeLonglong), agg.schema.Columns[i], val)
proj.Exprs[pos] = ifNullFunc
}
proj.SetChildren(apply)
p = proj
appendAddProjTraceStep(apply, proj, opt)
}
appendModifyAggTraceStep(outerPlan, apply, agg, sel, appendedGroupByCols, appendedAggFuncs, eqCondWithCorCol, opt)
return s.optimize(ctx, p, opt)
}
sel.Conditions = originalExpr
apply.CorCols = extractCorColumnsBySchema4LogicalPlan(apply.children[1], apply.children[0].Schema())
}
}
} else if sort, ok := innerPlan.(*LogicalSort); ok {
// Since we only pull up Selection, Projection, Aggregation, MaxOneRow,
// the top level Sort has no effect on the subquery's result.
innerPlan = sort.children[0]
apply.SetChildren(outerPlan, innerPlan)
appendRemoveSortTraceStep(sort, opt)
return s.optimize(ctx, p, opt)
}
}
NoOptimize:
newChildren := make([]LogicalPlan, 0, len(p.Children()))
for _, child := range p.Children() {
np, err := s.optimize(ctx, child, opt)
if err != nil {
return nil, err
}
newChildren = append(newChildren, np)
}
p.SetChildren(newChildren...)
return p, nil
}
func (*decorrelateSolver) name() string {
return "decorrelate"
}
func appendApplySimplifiedTraceStep(p *LogicalApply, j *LogicalJoin, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v simplified into %v_%v", plancodec.TypeApply, p.ID(), plancodec.TypeJoin, j.ID())
}
reason := func() string {
return fmt.Sprintf("%v_%v hasn't any corelated column, thus the inner plan is non-correlated", p.TP(), p.ID())
}
opt.appendStepToCurrent(p.ID(), p.TP(), reason, action)
}
func appendRemoveSelectionTraceStep(p LogicalPlan, s *LogicalSelection, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v removed from plan tree", s.TP(), s.ID())
}
reason := func() string {
return fmt.Sprintf("%v_%v's conditions have been pushed into %v_%v", s.TP(), s.ID(), p.TP(), p.ID())
}
opt.appendStepToCurrent(s.ID(), s.TP(), reason, action)
}
func appendRemoveMaxOneRowTraceStep(m *LogicalMaxOneRow, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v removed from plan tree", m.TP(), m.ID())
}
reason := func() string {
return ""
}
opt.appendStepToCurrent(m.ID(), m.TP(), reason, action)
}
func appendRemoveLimitTraceStep(limit *LogicalLimit, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v removed from plan tree", limit.TP(), limit.ID())
}
reason := func() string {
return fmt.Sprintf("%v_%v in 'exists' subquery need to remove in order to keep plan optimal", limit.TP(), limit.ID())
}
opt.appendStepToCurrent(limit.ID(), limit.TP(), reason, action)
}
func appendRemoveProjTraceStep(p *LogicalApply, proj *LogicalProjection, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v removed from plan tree", proj.TP(), proj.ID())
}
reason := func() string {
return fmt.Sprintf("%v_%v's columns all substituted into %v_%v", proj.TP(), proj.ID(), p.TP(), p.ID())
}
opt.appendStepToCurrent(proj.ID(), proj.TP(), reason, action)
}
func appendMoveProjTraceStep(p *LogicalApply, np LogicalPlan, proj *LogicalProjection, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v is moved as %v_%v's parent", proj.TP(), proj.ID(), np.TP(), np.ID())
}
reason := func() string {
return fmt.Sprintf("%v_%v's join type is %v, not semi join", p.TP(), p.ID(), p.JoinType.String())
}
opt.appendStepToCurrent(proj.ID(), proj.TP(), reason, action)
}
func appendRemoveSortTraceStep(sort *LogicalSort, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v removed from plan tree", sort.TP(), sort.ID())
}
reason := func() string {
return ""
}
opt.appendStepToCurrent(sort.ID(), sort.TP(), reason, action)
}
func appendPullUpAggTraceStep(p *LogicalApply, np LogicalPlan, agg *LogicalAggregation, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v pulled up as %v_%v's parent, and %v_%v's join type becomes %v",
agg.TP(), agg.ID(), np.TP(), np.ID(), p.TP(), p.ID(), p.JoinType.String())
}
reason := func() string {
return fmt.Sprintf("%v_%v's functions haven't any group by items and %v_%v's join type isn't %v or %v, and hasn't any conditions",
agg.TP(), agg.ID(), p.TP(), p.ID(), InnerJoin.String(), LeftOuterJoin.String())
}
opt.appendStepToCurrent(agg.ID(), agg.TP(), reason, action)
}
func appendAddProjTraceStep(p *LogicalApply, proj *LogicalProjection, opt *logicalOptimizeOp) {
action := func() string {
return fmt.Sprintf("%v_%v is added as %v_%v's parent", proj.TP(), proj.ID(), p.TP(), p.ID())
}
reason := func() string {
return ""
}
opt.appendStepToCurrent(proj.ID(), proj.TP(), reason, action)
}
func appendModifyAggTraceStep(outerPlan LogicalPlan, p *LogicalApply, agg *LogicalAggregation, sel *LogicalSelection,
appendedGroupByCols *expression.Schema, appendedAggFuncs []*aggregation.AggFuncDesc,
eqCondWithCorCol []*expression.ScalarFunction, opt *logicalOptimizeOp) {
action := func() string {
buffer := bytes.NewBufferString(fmt.Sprintf("%v_%v's groupby items added [", agg.TP(), agg.ID()))
for i, col := range appendedGroupByCols.Columns {
if i > 0 {
buffer.WriteString(",")
}
buffer.WriteString(col.String())
}
buffer.WriteString("], and functions added [")
for i, f := range appendedAggFuncs {
if i > 0 {
buffer.WriteString(",")
}
buffer.WriteString(f.String())
}
buffer.WriteString(fmt.Sprintf("], and %v_%v's conditions added [", p.TP(), p.ID()))
for i, cond := range eqCondWithCorCol {
if i > 0 {
buffer.WriteString(",")
}
buffer.WriteString(cond.String())
}
buffer.WriteString("]")
return buffer.String()
}
reason := func() string {
buffer := bytes.NewBufferString(fmt.Sprintf("%v_%v's equal conditions [", sel.TP(), sel.ID()))
for i, cond := range eqCondWithCorCol {
if i > 0 {
buffer.WriteString(",")
}
buffer.WriteString(cond.String())
}
buffer.WriteString(fmt.Sprintf("] are correlated to %v_%v and pulled up as %v_%v's join key",
outerPlan.TP(), outerPlan.ID(), p.TP(), p.ID()))
return buffer.String()
}
opt.appendStepToCurrent(agg.ID(), agg.TP(), reason, action)
}
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