tidb stats_info 源码
tidb stats_info 代码
文件路径：/planner/property/stats_info.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 property
import (
"fmt"
"github.com/pingcap/tidb/statistics"
)
// GroupNDV stores the NDV of a group of columns.
type GroupNDV struct {
// Cols are the UniqueIDs of columns.
Cols []int64
NDV float64
}
// ToString prints GroupNDV slice. It is only used for test.
func ToString(ndvs []GroupNDV) string {
return fmt.Sprintf("%v", ndvs)
}
// StatsInfo stores the basic information of statistics for the plan's output. It is used for cost estimation.
type StatsInfo struct {
RowCount float64
// Column.UniqueID -> NDV
ColNDVs map[int64]float64
HistColl *statistics.HistColl
// StatsVersion indicates the statistics version of a table.
// If the StatsInfo is calculated using the pseudo statistics on a table, StatsVersion will be PseudoVersion.
StatsVersion uint64
// GroupNDVs stores the NDV of column groups.
GroupNDVs []GroupNDV
}
// String implements fmt.Stringer interface.
func (s *StatsInfo) String() string {
return fmt.Sprintf("count %v, ColNDVs %v", s.RowCount, s.ColNDVs)
}
// Count gets the RowCount in the StatsInfo.
func (s *StatsInfo) Count() int64 {
return int64(s.RowCount)
}
// Scale receives a selectivity and multiplies it with RowCount and NDV.
func (s *StatsInfo) Scale(factor float64) *StatsInfo {
profile := &StatsInfo{
RowCount: s.RowCount * factor,
ColNDVs: make(map[int64]float64, len(s.ColNDVs)),
HistColl: s.HistColl,
StatsVersion: s.StatsVersion,
GroupNDVs: make([]GroupNDV, len(s.GroupNDVs)),
}
for id, c := range s.ColNDVs {
profile.ColNDVs[id] = c * factor
}
for i, g := range s.GroupNDVs {
profile.GroupNDVs[i] = g
profile.GroupNDVs[i].NDV = g.NDV * factor
}
return profile
}
// ScaleByExpectCnt tries to Scale StatsInfo to an expectCnt which must be
// smaller than the derived cnt.
// TODO: try to use a better way to do this.
func (s *StatsInfo) ScaleByExpectCnt(expectCnt float64) *StatsInfo {
if expectCnt >= s.RowCount {
return s
}
if s.RowCount > 1.0 { // if s.RowCount is too small, it will cause overflow
return s.Scale(expectCnt / s.RowCount)
}
return s
}
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