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find_best_task.go
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find_best_task.go
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// 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package core
import (
"math"
"github.com/hanchuanchuan/goInception/expression"
"github.com/hanchuanchuan/goInception/infoschema"
"github.com/hanchuanchuan/goInception/model"
"github.com/hanchuanchuan/goInception/mysql"
"github.com/hanchuanchuan/goInception/planner/property"
"github.com/hanchuanchuan/goInception/types"
"github.com/hanchuanchuan/goInception/util/chunk"
"github.com/pingcap/errors"
)
const (
netWorkFactor = 1.5
netWorkStartFactor = 20.0
scanFactor = 2.0
descScanFactor = 2 * scanFactor
memoryFactor = 5.0
// 0.5 is the looking up agg context factor.
hashAggFactor = 1.2 + 0.5
selectionFactor = 0.8
distinctFactor = 0.8
cpuFactor = 0.9
distinctAggFactor = 1.6
createAggCtxFactor = 6
)
// wholeTaskTypes records all possible kinds of task that a plan can return. For Agg, TopN and Limit, we will try to get
// these tasks one by one.
var wholeTaskTypes = [...]property.TaskType{property.CopSingleReadTaskType, property.CopDoubleReadTaskType, property.RootTaskType}
var invalidTask = &rootTask{cst: math.MaxFloat64}
// getPropByOrderByItems will check if this sort property can be pushed or not. In order to simplify the problem, we only
// consider the case that all expression are columns and all of them are asc or desc.
func getPropByOrderByItems(items []*ByItems) (*property.PhysicalProperty, bool) {
desc := false
cols := make([]*expression.Column, 0, len(items))
for i, item := range items {
col, ok := item.Expr.(*expression.Column)
if !ok {
return nil, false
}
cols = append(cols, col)
desc = item.Desc
if i > 0 && item.Desc != items[i-1].Desc {
return nil, false
}
}
return &property.PhysicalProperty{Cols: cols, Desc: desc}, true
}
func (p *LogicalTableDual) findBestTask(prop *property.PhysicalProperty) (task, error) {
if !prop.IsEmpty() {
return invalidTask, nil
}
dual := PhysicalTableDual{RowCount: p.RowCount}.init(p.ctx, p.stats)
dual.SetSchema(p.schema)
return &rootTask{p: dual}, nil
}
// findBestTask implements LogicalPlan interface.
func (p *baseLogicalPlan) findBestTask(prop *property.PhysicalProperty) (bestTask task, err error) {
// If p is an inner plan in an IndexJoin, the IndexJoin will generate an inner plan by itself,
// and set inner child prop nil, so here we do nothing.
if prop == nil {
return nil, nil
}
// Look up the task with this prop in the task map.
// It's used to reduce double counting.
bestTask = p.getTask(prop)
if bestTask != nil {
return bestTask, nil
}
if prop.TaskTp != property.RootTaskType {
// Currently all plan cannot totally push down.
p.storeTask(prop, invalidTask)
return invalidTask, nil
}
bestTask = invalidTask
childTasks := make([]task, 0, len(p.children))
// If prop.enforced is true, cols of prop as parameter in exhaustPhysicalPlans should be nil
// And reset it for enforcing task prop and storing map<prop,task>
oldPropCols := prop.Cols
if prop.Enforced {
// First, get the bestTask without enforced prop
prop.Enforced = false
bestTask, err = p.findBestTask(prop)
if err != nil {
return nil, errors.Trace(err)
}
prop.Enforced = true
// Next, get the bestTask with enforced prop
prop.Cols = []*expression.Column{}
}
physicalPlans := p.self.exhaustPhysicalPlans(prop)
prop.Cols = oldPropCols
for _, pp := range physicalPlans {
// find best child tasks firstly.
childTasks = childTasks[:0]
for i, child := range p.children {
childTask, err := child.findBestTask(pp.getChildReqProps(i))
if err != nil {
return nil, errors.Trace(err)
}
if childTask != nil && childTask.invalid() {
break
}
childTasks = append(childTasks, childTask)
}
// This check makes sure that there is no invalid child task.
if len(childTasks) != len(p.children) {
continue
}
// combine best child tasks with parent physical plan.
curTask := pp.attach2Task(childTasks...)
// enforce curTask property
if prop.Enforced {
curTask = enforceProperty(prop, curTask, p.basePlan.ctx)
}
// get the most efficient one.
if curTask.cost() < bestTask.cost() {
bestTask = curTask
}
}
p.storeTask(prop, bestTask)
return bestTask, nil
}
// tryToGetMemTask will check if this table is a mem table. If it is, it will produce a task.
func (ds *DataSource) tryToGetMemTask(prop *property.PhysicalProperty) (task task, err error) {
if !prop.IsEmpty() {
return nil, nil
}
if !infoschema.IsMemoryDB(ds.DBName.L) {
return nil, nil
}
memTable := PhysicalMemTable{
DBName: ds.DBName,
Table: ds.tableInfo,
Columns: ds.Columns,
TableAsName: ds.TableAsName,
}.init(ds.ctx, ds.stats)
memTable.SetSchema(ds.schema)
// Stop to push down these conditions.
var retPlan PhysicalPlan = memTable
if len(ds.pushedDownConds) > 0 {
sel := PhysicalSelection{
Conditions: ds.pushedDownConds,
}.init(ds.ctx, ds.stats)
sel.SetChildren(memTable)
retPlan = sel
}
return &rootTask{p: retPlan}, nil
}
// tryToGetDualTask will check if the push down predicate has false constant. If so, it will return table dual.
func (ds *DataSource) tryToGetDualTask() (task, error) {
for _, cond := range ds.pushedDownConds {
if con, ok := cond.(*expression.Constant); ok && con.DeferredExpr == nil {
result, err := expression.EvalBool(ds.ctx, []expression.Expression{cond}, chunk.Row{})
if err != nil {
return nil, errors.Trace(err)
}
if !result {
dual := PhysicalTableDual{}.init(ds.ctx, ds.stats)
dual.SetSchema(ds.schema)
return &rootTask{
p: dual,
}, nil
}
}
}
return nil, nil
}
// findBestTask implements the PhysicalPlan interface.
// It will enumerate all the available indices and choose a plan with least cost.
func (ds *DataSource) findBestTask(prop *property.PhysicalProperty) (t task, err error) {
// If ds is an inner plan in an IndexJoin, the IndexJoin will generate an inner plan by itself,
// and set inner child prop nil, so here we do nothing.
if prop == nil {
return nil, nil
}
t = ds.getTask(prop)
if t != nil {
return
}
// If prop.enforced is true, the prop.cols need to be set nil for ds.findBestTask.
// Before function return, reset it for enforcing task prop and storing map<prop,task>.
oldPropCols := prop.Cols
if prop.Enforced {
// First, get the bestTask without enforced prop
prop.Enforced = false
t, err = ds.findBestTask(prop)
if err != nil {
return nil, errors.Trace(err)
}
prop.Enforced = true
if t != invalidTask {
ds.storeTask(prop, t)
return
}
// Next, get the bestTask with enforced prop
prop.Cols = []*expression.Column{}
}
defer func() {
if err != nil {
return
}
if prop.Enforced {
prop.Cols = oldPropCols
t = enforceProperty(prop, t, ds.basePlan.ctx)
}
ds.storeTask(prop, t)
}()
t, err = ds.tryToGetDualTask()
if err != nil || t != nil {
return t, errors.Trace(err)
}
t, err = ds.tryToGetMemTask(prop)
if err != nil || t != nil {
return t, errors.Trace(err)
}
t = invalidTask
for _, path := range ds.possibleAccessPaths {
// if we already know the range of the scan is empty, just return a TableDual
if len(path.ranges) == 0 && !ds.ctx.GetSessionVars().StmtCtx.UseCache {
dual := PhysicalTableDual{}.init(ds.ctx, ds.stats)
dual.SetSchema(ds.schema)
return &rootTask{
p: dual,
}, nil
}
if path.isTablePath {
tblTask, err := ds.convertToTableScan(prop, path)
if err != nil {
return nil, errors.Trace(err)
}
if tblTask.cost() < t.cost() {
t = tblTask
}
continue
}
// We will use index to generate physical plan if:
// this path's access cond is not nil or
// we have prop to match or
// this index is forced to choose.
if len(path.accessConds) > 0 || len(prop.Cols) > 0 || path.forced {
idxTask, err := ds.convertToIndexScan(prop, path)
if err != nil {
return nil, errors.Trace(err)
}
if idxTask.cost() < t.cost() {
t = idxTask
}
}
}
return
}
func isCoveringIndex(columns []*model.ColumnInfo, indexColumns []*model.IndexColumn, pkIsHandle bool) bool {
for _, colInfo := range columns {
if pkIsHandle && mysql.HasPriKeyFlag(colInfo.Flag) {
continue
}
if colInfo.ID == model.ExtraHandleID {
continue
}
isIndexColumn := false
for _, indexCol := range indexColumns {
isFullLen := indexCol.Length == types.UnspecifiedLength || indexCol.Length == colInfo.Flen
if colInfo.Name.L == indexCol.Name.L && isFullLen {
isIndexColumn = true
break
}
}
if !isIndexColumn {
return false
}
}
return true
}
// If there is a table reader which needs to keep order, we should append a pk to table scan.
func (ts *PhysicalTableScan) appendExtraHandleCol(ds *DataSource) {
if len(ds.schema.TblID2Handle) > 0 {
return
}
pkInfo := model.NewExtraHandleColInfo()
ts.Columns = append(ts.Columns, pkInfo)
handleCol := ds.newExtraHandleSchemaCol()
ts.schema.Append(handleCol)
ts.schema.TblID2Handle[ds.tableInfo.ID] = []*expression.Column{handleCol}
}
// convertToIndexScan converts the DataSource to index scan with idx.
func (ds *DataSource) convertToIndexScan(prop *property.PhysicalProperty, path *accessPath) (task task, err error) {
idx := path.index
is := PhysicalIndexScan{
Table: ds.tableInfo,
TableAsName: ds.TableAsName,
DBName: ds.DBName,
Columns: ds.Columns,
Index: idx,
IdxCols: path.idxCols,
IdxColLens: path.idxColLens,
AccessCondition: path.accessConds,
Ranges: path.ranges,
filterCondition: path.indexFilters,
dataSourceSchema: ds.schema,
isPartition: ds.isPartition,
physicalTableID: ds.physicalTableID,
}.init(ds.ctx)
statsTbl := ds.statisticTable
if statsTbl.Indices[idx.ID] != nil {
is.Hist = &statsTbl.Indices[idx.ID].Histogram
}
rowCount := path.countAfterAccess
cop := &copTask{indexPlan: is}
if !isCoveringIndex(is.Columns, is.Index.Columns, is.Table.PKIsHandle) {
// If it's parent requires single read task, return max cost.
if prop.TaskTp == property.CopSingleReadTaskType {
return invalidTask, nil
}
// On this way, it's double read case.
ts := PhysicalTableScan{
Columns: ds.Columns,
Table: is.Table,
isPartition: ds.isPartition,
physicalTableID: ds.physicalTableID,
}.init(ds.ctx)
ts.SetSchema(ds.schema.Clone())
cop.tablePlan = ts
} else if prop.TaskTp == property.CopDoubleReadTaskType {
// If it's parent requires double read task, return max cost.
return invalidTask, nil
}
is.initSchema(ds.id, idx, cop.tablePlan != nil)
// Check if this plan matches the property.
matchProperty := false
if !prop.IsEmpty() {
for i, col := range idx.Columns {
// not matched
if col.Name.L == prop.Cols[0].ColName.L {
matchProperty = matchIndicesProp(idx.Columns[i:], prop.Cols)
break
} else if i >= path.eqCondCount {
break
}
}
}
// Only use expectedCnt when it's smaller than the count we calculated.
// e.g. IndexScan(count1)->After Filter(count2). The `ds.stats.RowCount` is count2. count1 is the one we need to calculate
// If expectedCnt and count2 are both zero and we go into the below `if` block, the count1 will be set to zero though it's shouldn't be.
if (matchProperty || prop.IsEmpty()) && prop.ExpectedCnt < ds.stats.RowCount {
selectivity := ds.stats.RowCount / path.countAfterAccess
rowCount = math.Min(prop.ExpectedCnt/selectivity, rowCount)
}
is.stats = property.NewSimpleStats(rowCount)
is.stats.UsePseudoStats = ds.statisticTable.Pseudo
cop.cst = rowCount * scanFactor
task = cop
if matchProperty {
if prop.Desc {
is.Desc = true
cop.cst = rowCount * descScanFactor
}
if cop.tablePlan != nil {
cop.tablePlan.(*PhysicalTableScan).appendExtraHandleCol(ds)
}
cop.keepOrder = true
is.KeepOrder = true
is.addPushedDownSelection(cop, ds, prop.ExpectedCnt, path)
} else {
expectedCnt := math.MaxFloat64
if prop.IsEmpty() {
expectedCnt = prop.ExpectedCnt
} else {
return invalidTask, nil
}
is.addPushedDownSelection(cop, ds, expectedCnt, path)
}
if prop.TaskTp == property.RootTaskType {
task = finishCopTask(ds.ctx, task)
} else if _, ok := task.(*rootTask); ok {
return invalidTask, nil
}
return task, nil
}
// TODO: refactor this part, we should not call Clone in fact.
func (is *PhysicalIndexScan) initSchema(id int, idx *model.IndexInfo, isDoubleRead bool) {
indexCols := make([]*expression.Column, 0, len(idx.Columns))
for _, col := range idx.Columns {
colFound := is.dataSourceSchema.FindColumnByName(col.Name.L)
if colFound == nil {
colFound = &expression.Column{ColName: col.Name, UniqueID: is.ctx.GetSessionVars().AllocPlanColumnID()}
} else {
colFound = colFound.Clone().(*expression.Column)
}
indexCols = append(indexCols, colFound)
}
setHandle := false
for _, col := range is.Columns {
if (mysql.HasPriKeyFlag(col.Flag) && is.Table.PKIsHandle) || col.ID == model.ExtraHandleID {
indexCols = append(indexCols, is.dataSourceSchema.FindColumnByName(col.Name.L))
setHandle = true
break
}
}
// If it's double read case, the first index must return handle. So we should add extra handle column
// if there isn't a handle column.
if isDoubleRead && !setHandle {
indexCols = append(indexCols, &expression.Column{ID: model.ExtraHandleID, ColName: model.ExtraHandleName, UniqueID: is.ctx.GetSessionVars().AllocPlanColumnID()})
}
is.SetSchema(expression.NewSchema(indexCols...))
}
func (is *PhysicalIndexScan) addPushedDownSelection(copTask *copTask, p *DataSource, expectedCnt float64, path *accessPath) {
// Add filter condition to table plan now.
indexConds, tableConds := path.indexFilters, path.tableFilters
if indexConds != nil {
copTask.cst += copTask.count() * cpuFactor
count := path.countAfterAccess
if count >= 1.0 {
selectivity := path.countAfterIndex / path.countAfterAccess
count = is.stats.RowCount * selectivity
}
stats := &property.StatsInfo{RowCount: count}
indexSel := PhysicalSelection{Conditions: indexConds}.init(is.ctx, stats)
indexSel.SetChildren(is)
copTask.indexPlan = indexSel
}
if tableConds != nil {
copTask.finishIndexPlan()
copTask.cst += copTask.count() * cpuFactor
tableSel := PhysicalSelection{Conditions: tableConds}.init(is.ctx, p.stats.ScaleByExpectCnt(expectedCnt))
tableSel.SetChildren(copTask.tablePlan)
copTask.tablePlan = tableSel
}
}
func matchIndicesProp(idxCols []*model.IndexColumn, propCols []*expression.Column) bool {
if len(idxCols) < len(propCols) {
return false
}
for i, col := range propCols {
if idxCols[i].Length != types.UnspecifiedLength || col.ColName.L != idxCols[i].Name.L {
return false
}
}
return true
}
func splitIndexFilterConditions(conditions []expression.Expression, indexColumns []*model.IndexColumn,
table *model.TableInfo) (indexConds, tableConds []expression.Expression) {
var pkName model.CIStr
if table.PKIsHandle {
pkInfo := table.GetPkColInfo()
if pkInfo != nil {
pkName = pkInfo.Name
}
}
var indexConditions, tableConditions []expression.Expression
for _, cond := range conditions {
if checkIndexCondition(cond, indexColumns, pkName) {
indexConditions = append(indexConditions, cond)
} else {
tableConditions = append(tableConditions, cond)
}
}
return indexConditions, tableConditions
}
// checkIndexCondition will check whether all columns of condition is index columns or primary key column.
func checkIndexCondition(condition expression.Expression, indexColumns []*model.IndexColumn, pkName model.CIStr) bool {
cols := expression.ExtractColumns(condition)
for _, col := range cols {
if pkName.L == col.ColName.L {
continue
}
isIndexColumn := false
for _, indCol := range indexColumns {
if col.ColName.L == indCol.Name.L && indCol.Length == types.UnspecifiedLength {
isIndexColumn = true
break
}
}
if !isIndexColumn {
return false
}
}
return true
}
// convertToTableScan converts the DataSource to table scan.
func (ds *DataSource) convertToTableScan(prop *property.PhysicalProperty, path *accessPath) (task task, err error) {
// It will be handled in convertToIndexScan.
if prop.TaskTp == property.CopDoubleReadTaskType {
return invalidTask, nil
}
ts := PhysicalTableScan{
Table: ds.tableInfo,
Columns: ds.Columns,
TableAsName: ds.TableAsName,
DBName: ds.DBName,
isPartition: ds.isPartition,
physicalTableID: ds.physicalTableID,
}.init(ds.ctx)
ts.SetSchema(ds.schema)
var pkCol *expression.Column
if ts.Table.PKIsHandle {
if pkColInfo := ts.Table.GetPkColInfo(); pkColInfo != nil {
pkCol = expression.ColInfo2Col(ts.schema.Columns, pkColInfo)
if ds.statisticTable.Columns[pkColInfo.ID] != nil {
ts.Hist = &ds.statisticTable.Columns[pkColInfo.ID].Histogram
}
}
}
ts.Ranges = path.ranges
ts.AccessCondition, ts.filterCondition = path.accessConds, path.tableFilters
rowCount := path.countAfterAccess
copTask := &copTask{
tablePlan: ts,
indexPlanFinished: true,
}
task = copTask
matchProperty := len(prop.Cols) == 1 && pkCol != nil && prop.Cols[0].Equal(nil, pkCol)
// Only use expectedCnt when it's smaller than the count we calculated.
// e.g. IndexScan(count1)->After Filter(count2). The `ds.stats.RowCount` is count2. count1 is the one we need to calculate
// If expectedCnt and count2 are both zero and we go into the below `if` block, the count1 will be set to zero though it's shouldn't be.
if (matchProperty || prop.IsEmpty()) && prop.ExpectedCnt < ds.stats.RowCount {
selectivity := ds.stats.RowCount / rowCount
rowCount = math.Min(prop.ExpectedCnt/selectivity, rowCount)
}
ts.stats = property.NewSimpleStats(rowCount)
ts.stats.UsePseudoStats = ds.statisticTable.Pseudo
copTask.cst = rowCount * scanFactor
if matchProperty {
if prop.Desc {
ts.Desc = true
copTask.cst = rowCount * descScanFactor
}
ts.KeepOrder = true
copTask.keepOrder = true
ts.addPushedDownSelection(copTask, ds.stats.ScaleByExpectCnt(prop.ExpectedCnt))
} else {
expectedCnt := math.MaxFloat64
if prop.IsEmpty() {
expectedCnt = prop.ExpectedCnt
} else {
return invalidTask, nil
}
ts.addPushedDownSelection(copTask, ds.stats.ScaleByExpectCnt(expectedCnt))
}
if prop.TaskTp == property.RootTaskType {
task = finishCopTask(ds.ctx, task)
} else if _, ok := task.(*rootTask); ok {
return invalidTask, nil
}
return task, nil
}
func (ts *PhysicalTableScan) addPushedDownSelection(copTask *copTask, stats *property.StatsInfo) {
// Add filter condition to table plan now.
if len(ts.filterCondition) > 0 {
copTask.cst += copTask.count() * cpuFactor
sel := PhysicalSelection{Conditions: ts.filterCondition}.init(ts.ctx, stats)
sel.SetChildren(ts)
copTask.tablePlan = sel
}
}