tidb enforcer_rules 代码
文件路径：/planner/cascades/enforcer_rules.go
/ Copyright 2018 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 cascades
import (
"math"
plannercore "github.com/pingcap/tidb/planner/core"
"github.com/pingcap/tidb/planner/implementation"
"github.com/pingcap/tidb/planner/memo"
"github.com/pingcap/tidb/planner/property"
"github.com/pingcap/tidb/planner/util"
)
/ Enforcer defines the interface for enforcer rules.
type Enforcer interface {
/ NewProperty generates relaxed property with the help of enforcer.
NewProperty(prop *property.PhysicalProperty) (newProp *property.PhysicalProperty)
/ OnEnforce adds physical operators on top of child implementation to satisfy
/ required physical property.
OnEnforce(reqProp *property.PhysicalProperty, child memo.Implementation) (impl memo.Implementation)
/ GetEnforceCost calculates cost of enforcing required physical property.
GetEnforceCost(g *memo.Group) float64
}
/ GetEnforcerRules gets all candidate enforcer rules based
/ on required physical property.
func GetEnforcerRules(g *memo.Group, prop *property.PhysicalProperty) (enforcers []Enforcer) {
if g.EngineType != memo.EngineTiDB {
return
}
if !prop.IsSortItemEmpty() {
enforcers = append(enforcers, orderEnforcer)
}
return
}
/ OrderEnforcer enforces order property on child implementation.
type OrderEnforcer struct {
}
var orderEnforcer = &OrderEnforcer{}
/ NewProperty removes order property from required physical property.
func (*OrderEnforcer) NewProperty(_ *property.PhysicalProperty) (newProp *property.PhysicalProperty) {
/ Order property cannot be empty now.
newProp = &property.PhysicalProperty{ExpectedCnt: math.MaxFloat64}
return
}
/ OnEnforce adds sort operator to satisfy required order property.
func (*OrderEnforcer) OnEnforce(reqProp *property.PhysicalProperty, child memo.Implementation) (impl memo.Implementation) {
childPlan := child.GetPlan()
sort := plannercore.PhysicalSort{
ByItems: make([]*util.ByItems, 0, len(reqProp.SortItems)),
}.Init(childPlan.SCtx(), childPlan.Stats(), childPlan.SelectBlockOffset(), &property.PhysicalProperty{ExpectedCnt: math.MaxFloat64})
for _, item := range reqProp.SortItems {
item := &util.ByItems{
Expr: item.Col,
Desc: item.Desc,
}
sort.ByItems = append(sort.ByItems, item)
}
impl = implementation.NewSortImpl(sort).AttachChildren(child)
return
}
/ GetEnforceCost calculates cost of sort operator.
func (*OrderEnforcer) GetEnforceCost(g *memo.Group) float64 {
/ We need a SessionCtx to calculate the cost of a sort.
sctx := g.Equivalents.Front().Value.(*memo.GroupExpr).ExprNode.SCtx()
sort := plannercore.PhysicalSort{}.Init(sctx, g.Prop.Stats, 0, nil)
cost := sort.GetCost(g.Prop.Stats.RowCount, g.Prop.Schema)
return cost
}