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physical_property.go 3.25 KB
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// 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,
// See the License for the specific language governing permissions and
// limitations under the License.
package property
import (
"fmt"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/util/codec"
)
// PhysicalProperty stands for the required physical property by parents.
// It contains the orders, if the order is desc and the task types.
type PhysicalProperty struct {
Cols []*expression.Column
Desc bool
// TaskTp means the type of task that an operator requires.
//
// It needs to be specified because two different tasks can't be compared
// with cost directly. e.g. If a copTask takes less cost than a rootTask,
// we can't sure that we must choose the former one. Because the copTask
// must be finished and increase its cost in sometime, but we can't make
// sure the finishing time. So the best way to let the comparison fair is
// to add TaskType to required property.
TaskTp TaskType
// ExpectedCnt means this operator may be closed after fetching ExpectedCnt
// records.
ExpectedCnt float64
// hashcode stores the hash code of a PhysicalProperty, will be lazily
// calculated when function "HashCode()" being called.
hashcode []byte
// whether need to enforce property.
Enforced bool
}
// AllColsFromSchema checks whether all the columns needed by this physical
// property can be found in the given schema.
func (p *PhysicalProperty) AllColsFromSchema(schema *expression.Schema) bool {
return schema.ColumnsIndices(p.Cols) != nil
}
// IsPrefix checks whether the order property is the prefix of another.
func (p *PhysicalProperty) IsPrefix(prop *PhysicalProperty) bool {
if len(p.Cols) > len(prop.Cols) || p.Desc != prop.Desc {
return false
}
for i := range p.Cols {
if !p.Cols[i].Equal(nil, prop.Cols[i]) {
return false
}
}
return true
}
// IsEmpty checks whether the order property is empty.
func (p *PhysicalProperty) IsEmpty() bool {
return len(p.Cols) == 0
}
// HashCode calculates hash code for a PhysicalProperty object.
func (p *PhysicalProperty) HashCode() []byte {
if p.hashcode != nil {
return p.hashcode
}
hashcodeSize := 8 + 8 + 8 + 16*len(p.Cols) + 8
p.hashcode = make([]byte, 0, hashcodeSize)
if p.Desc {
p.hashcode = codec.EncodeInt(p.hashcode, 1)
} else {
p.hashcode = codec.EncodeInt(p.hashcode, 0)
}
if p.Enforced {
p.hashcode = codec.EncodeInt(p.hashcode, 1)
} else {
p.hashcode = codec.EncodeInt(p.hashcode, 0)
}
p.hashcode = codec.EncodeInt(p.hashcode, int64(p.TaskTp))
p.hashcode = codec.EncodeFloat(p.hashcode, p.ExpectedCnt)
for i, length := 0, len(p.Cols); i < length; i++ {
p.hashcode = append(p.hashcode, p.Cols[i].HashCode(nil)...)
}
return p.hashcode
}
// String implements fmt.Stringer interface. Just for test.
func (p *PhysicalProperty) String() string {
return fmt.Sprintf("Prop{cols: %v, desc: %v, TaskTp: %s, expectedCount: %v}", p.Cols, p.Desc, p.TaskTp, p.ExpectedCnt)
}
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