gitea/vendor/github.com/pingcap/tidb/optimizer/plan/cost.go
Thomas Boerger b6a95a8cb3 Integrate public as bindata optionally (#293)
* Dropped unused codekit config

* Integrated dynamic and static bindata for public

* Ignore public bindata

* Add a general generate make task

* Integrated flexible public assets into web command

* Updated vendoring, added all missiong govendor deps

* Made the linter happy with the bindata and dynamic code

* Moved public bindata definition to modules directory

* Ignoring the new bindata path now

* Updated to the new public modules import path

* Updated public bindata command and drop the new prefix
2016-11-30 00:26:36 +08:00

110 lines
2.7 KiB
Go

// Copyright 2015 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 plan
import (
"math"
)
// Pre-defined cost factors.
const (
FullRangeCount = 10000
HalfRangeCount = 4000
MiddleRangeCount = 100
RowCost = 1.0
IndexCost = 2.0
SortCost = 2.0
FilterRate = 0.5
)
// CostEstimator estimates the cost of a plan.
type costEstimator struct {
}
// Enter implements Visitor Enter interface.
func (c *costEstimator) Enter(p Plan) (Plan, bool) {
return p, false
}
// Leave implements Visitor Leave interface.
func (c *costEstimator) Leave(p Plan) (Plan, bool) {
switch v := p.(type) {
case *IndexScan:
c.indexScan(v)
case *Limit:
v.rowCount = v.Src().RowCount()
v.startupCost = v.Src().StartupCost()
v.totalCost = v.Src().TotalCost()
case *SelectFields:
if v.Src() != nil {
v.startupCost = v.Src().StartupCost()
v.rowCount = v.Src().RowCount()
v.totalCost = v.Src().TotalCost()
}
case *SelectLock:
v.startupCost = v.Src().StartupCost()
v.rowCount = v.Src().RowCount()
v.totalCost = v.Src().TotalCost()
case *Sort:
// Sort plan must retrieve all the rows before returns the first row.
v.startupCost = v.Src().TotalCost() + v.Src().RowCount()*SortCost
if v.limit == 0 {
v.rowCount = v.Src().RowCount()
} else {
v.rowCount = math.Min(v.Src().RowCount(), v.limit)
}
v.totalCost = v.startupCost + v.rowCount*RowCost
case *TableScan:
c.tableScan(v)
}
return p, true
}
func (c *costEstimator) tableScan(v *TableScan) {
var rowCount float64 = FullRangeCount
for _, con := range v.AccessConditions {
rowCount *= guesstimateFilterRate(con)
}
v.startupCost = 0
if v.limit == 0 {
// limit is zero means no limit.
v.rowCount = rowCount
} else {
v.rowCount = math.Min(rowCount, v.limit)
}
v.totalCost = v.rowCount * RowCost
}
func (c *costEstimator) indexScan(v *IndexScan) {
var rowCount float64 = FullRangeCount
for _, con := range v.AccessConditions {
rowCount *= guesstimateFilterRate(con)
}
v.startupCost = 0
if v.limit == 0 {
// limit is zero means no limit.
v.rowCount = rowCount
} else {
v.rowCount = math.Min(rowCount, v.limit)
}
v.totalCost = v.rowCount * RowCost
}
// EstimateCost estimates the cost of the plan.
func EstimateCost(p Plan) float64 {
var estimator costEstimator
p.Accept(&estimator)
return p.TotalCost()
}