102 lines
2.3 KiB
Go
102 lines
2.3 KiB
Go
// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package plan
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import "github.com/juju/errors"
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// Alternatives returns multiple alternative plans that
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// can be picked base on their cost.
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func Alternatives(p Plan) ([]Plan, error) {
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var plans []Plan
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switch x := p.(type) {
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case nil:
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case *TableScan:
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plans = tableScanAlternatives(x)
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case WithSrcPlan:
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var err error
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plans, err = planWithSrcAlternatives(x)
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if err != nil {
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return nil, errors.Trace(err)
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}
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case *Prepare:
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case *Execute:
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case *Deallocate:
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default:
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return nil, ErrUnsupportedType.Gen("Unknown plan %T", p)
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}
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for _, val := range plans {
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err := refine(val)
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if err != nil {
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return nil, errors.Trace(err)
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}
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}
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return plans, nil
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}
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// tableScanAlternatives returns all index plans from the same table.
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func tableScanAlternatives(p *TableScan) []Plan {
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var alts []Plan
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for _, v := range p.Table.Indices {
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fullRange := &IndexRange{
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LowVal: []interface{}{nil},
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HighVal: []interface{}{MaxVal},
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}
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ip := &IndexScan{
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Index: v,
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Table: p.Table,
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Ranges: []*IndexRange{fullRange},
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}
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ip.SetFields(p.Fields())
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alts = append(alts, ip)
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}
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return alts
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}
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// planWithSrcAlternatives shallow copies the WithSrcPlan,
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// and set its src to src alternatives.
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func planWithSrcAlternatives(p WithSrcPlan) ([]Plan, error) {
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srcs, err := Alternatives(p.Src())
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if err != nil {
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return nil, errors.Trace(err)
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}
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for i, val := range srcs {
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alt := shallowCopy(p)
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alt.SetSrc(val)
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srcs[i] = alt
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}
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return srcs, nil
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}
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func shallowCopy(p WithSrcPlan) WithSrcPlan {
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var copied WithSrcPlan
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switch x := p.(type) {
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case *Filter:
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n := *x
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copied = &n
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case *SelectLock:
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n := *x
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copied = &n
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case *SelectFields:
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n := *x
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copied = &n
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case *Sort:
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n := *x
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copied = &n
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case *Limit:
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n := *x
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copied = &n
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}
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return copied
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}
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