74 lines
2.1 KiB
Go
74 lines
2.1 KiB
Go
// Copyright 2018 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 property
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import (
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"fmt"
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"github.com/pingcap/tidb/statistics"
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)
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// StatsInfo stores the basic information of statistics for the plan's output. It is used for cost estimation.
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type StatsInfo struct {
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RowCount float64
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Cardinality []float64
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HistColl *statistics.HistColl
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// UsePseudoStats indicates whether the StatsInfo is calculated using the
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// pseudo statistics on a table.
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UsePseudoStats bool
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}
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// NewSimpleStats creates a simple StatsInfo with rowCount.
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func NewSimpleStats(rowCount float64) *StatsInfo {
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return &StatsInfo{RowCount: rowCount}
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}
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// String implements fmt.Stringer interface.
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func (s *StatsInfo) String() string {
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return fmt.Sprintf("count %v, Cardinality %v", s.RowCount, s.Cardinality)
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}
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// Count gets the RowCount in the StatsInfo.
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func (s *StatsInfo) Count() int64 {
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return int64(s.RowCount)
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}
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// Scale receives a selectivity and multiplies it with RowCount and Cardinality.
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func (s *StatsInfo) Scale(factor float64) *StatsInfo {
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profile := &StatsInfo{
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RowCount: s.RowCount * factor,
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Cardinality: make([]float64, len(s.Cardinality)),
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HistColl: s.HistColl,
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UsePseudoStats: s.UsePseudoStats,
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}
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for i := range profile.Cardinality {
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profile.Cardinality[i] = s.Cardinality[i] * factor
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}
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return profile
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}
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// ScaleByExpectCnt tries to Scale StatsInfo to an expectCnt which must be
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// smaller than the derived cnt.
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// TODO: try to use a better way to do this.
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func (s *StatsInfo) ScaleByExpectCnt(expectCnt float64) *StatsInfo {
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if expectCnt > s.RowCount {
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return s
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}
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if s.RowCount > 1.0 { // if s.RowCount is too small, it will cause overflow
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return s.Scale(expectCnt / s.RowCount)
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}
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return s
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}
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