tidb/executor/analyze.go

// Copyright 2017 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 executor

import (
	"bytes"
	"context"
	"fmt"
	"math"
	"math/rand"
	"runtime"
	"sort"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"github.com/cznic/mathutil"
	"github.com/pingcap/errors"
	"github.com/pingcap/failpoint"
	"github.com/pingcap/parser/ast"
	"github.com/pingcap/parser/model"
	"github.com/pingcap/parser/mysql"
	"github.com/pingcap/parser/terror"
	"github.com/pingcap/tidb/distsql"
	"github.com/pingcap/tidb/domain"
	"github.com/pingcap/tidb/infoschema"
	"github.com/pingcap/tidb/kv"
	"github.com/pingcap/tidb/metrics"
	"github.com/pingcap/tidb/planner/core"
	"github.com/pingcap/tidb/sessionctx"
	"github.com/pingcap/tidb/sessionctx/variable"
	"github.com/pingcap/tidb/statistics"
	"github.com/pingcap/tidb/store/tikv"
	"github.com/pingcap/tidb/table"
	"github.com/pingcap/tidb/tablecodec"
	"github.com/pingcap/tidb/types"
	"github.com/pingcap/tidb/util/chunk"
	"github.com/pingcap/tidb/util/codec"
	"github.com/pingcap/tidb/util/logutil"
	"github.com/pingcap/tidb/util/ranger"
	"github.com/pingcap/tidb/util/sqlexec"
	"github.com/pingcap/tipb/go-tipb"
	"go.uber.org/zap"
)

var _ Executor = &AnalyzeExec{}

// AnalyzeExec represents Analyze executor.
type AnalyzeExec struct {
	baseExecutor
	tasks []*analyzeTask
	wg    *sync.WaitGroup
}

var (
	// RandSeed is the seed for randing package.
	// It's public for test.
	RandSeed = int64(1)
)

const (
	maxRegionSampleSize = 1000
	maxSketchSize       = 10000
)

// Next implements the Executor Next interface.
func (e *AnalyzeExec) Next(ctx context.Context, req *chunk.Chunk) error {
	concurrency, err := getBuildStatsConcurrency(e.ctx)
	if err != nil {
		return err
	}
	taskCh := make(chan *analyzeTask, len(e.tasks))
	resultCh := make(chan analyzeResult, len(e.tasks))
	e.wg.Add(concurrency)
	for i := 0; i < concurrency; i++ {
		go e.analyzeWorker(taskCh, resultCh, i == 0)
	}
	for _, task := range e.tasks {
		statistics.AddNewAnalyzeJob(task.job)
	}
	for _, task := range e.tasks {
		taskCh <- task
	}
	close(taskCh)
	statsHandle := domain.GetDomain(e.ctx).StatsHandle()
	panicCnt := 0
	for panicCnt < concurrency {
		result, ok := <-resultCh
		if !ok {
			break
		}
		if result.Err != nil {
			err = result.Err
			if err == errAnalyzeWorkerPanic {
				panicCnt++
			} else {
				logutil.Logger(ctx).Error("analyze failed", zap.Error(err))
			}
			result.job.Finish(true)
			continue
		}
		for i, hg := range result.Hist {
			err1 := statsHandle.SaveStatsToStorage(result.TableID.PersistID, result.Count, result.IsIndex, hg, result.Cms[i], 1)
			if err1 != nil {
				err = err1
				logutil.Logger(ctx).Error("save stats to storage failed", zap.Error(err))
				result.job.Finish(true)
				continue
			}
		}
		if err1 := statsHandle.SaveExtendedStatsToStorage(result.TableID.PersistID, result.ExtStats, false); err1 != nil {
			err = err1
			logutil.Logger(ctx).Error("save extended stats to storage failed", zap.Error(err))
			result.job.Finish(true)
		} else {
			result.job.Finish(false)
		}
	}
	for _, task := range e.tasks {
		statistics.MoveToHistory(task.job)
	}
	if err != nil {
		return err
	}
	return statsHandle.Update(infoschema.GetInfoSchema(e.ctx))
}

func getBuildStatsConcurrency(ctx sessionctx.Context) (int, error) {
	sessionVars := ctx.GetSessionVars()
	concurrency, err := variable.GetSessionSystemVar(sessionVars, variable.TiDBBuildStatsConcurrency)
	if err != nil {
		return 0, err
	}
	c, err := strconv.ParseInt(concurrency, 10, 64)
	return int(c), err
}

type taskType int

const (
	colTask taskType = iota
	idxTask
	fastTask
	pkIncrementalTask
	idxIncrementalTask
)

type analyzeTask struct {
	taskType           taskType
	idxExec            *AnalyzeIndexExec
	colExec            *AnalyzeColumnsExec
	fastExec           *AnalyzeFastExec
	idxIncrementalExec *analyzeIndexIncrementalExec
	colIncrementalExec *analyzePKIncrementalExec
	job                *statistics.AnalyzeJob
}

var errAnalyzeWorkerPanic = errors.New("analyze worker panic")

func (e *AnalyzeExec) analyzeWorker(taskCh <-chan *analyzeTask, resultCh chan<- analyzeResult, isCloseChanThread bool) {
	var task *analyzeTask
	defer func() {
		if r := recover(); r != nil {
			buf := make([]byte, 4096)
			stackSize := runtime.Stack(buf, false)
			buf = buf[:stackSize]
			logutil.BgLogger().Error("analyze worker panicked", zap.String("stack", string(buf)))
			metrics.PanicCounter.WithLabelValues(metrics.LabelAnalyze).Inc()
			resultCh <- analyzeResult{
				Err: errAnalyzeWorkerPanic,
				job: task.job,
			}
		}
		e.wg.Done()
		if isCloseChanThread {
			e.wg.Wait()
			close(resultCh)
		}
	}()
	for {
		var ok bool
		task, ok = <-taskCh
		if !ok {
			break
		}
		task.job.Start()
		switch task.taskType {
		case colTask:
			task.colExec.job = task.job
			resultCh <- analyzeColumnsPushdown(task.colExec)
		case idxTask:
			task.idxExec.job = task.job
			resultCh <- analyzeIndexPushdown(task.idxExec)
		case fastTask:
			task.fastExec.job = task.job
			task.job.Start()
			for _, result := range analyzeFastExec(task.fastExec) {
				resultCh <- result
			}
		case pkIncrementalTask:
			task.colIncrementalExec.job = task.job
			resultCh <- analyzePKIncremental(task.colIncrementalExec)
		case idxIncrementalTask:
			task.idxIncrementalExec.job = task.job
			resultCh <- analyzeIndexIncremental(task.idxIncrementalExec)
		}
	}
}

func analyzeIndexPushdown(idxExec *AnalyzeIndexExec) analyzeResult {
	ranges := ranger.FullRange()
	// For single-column index, we do not load null rows from TiKV, so the built histogram would not include
	// null values, and its `NullCount` would be set by result of another distsql call to get null rows.
	// For multi-column index, we cannot define null for the rows, so we still use full range, and the rows
	// containing null fields would exist in built histograms. Note that, the `NullCount` of histograms for
	// multi-column index is always 0 then.
	if len(idxExec.idxInfo.Columns) == 1 {
		ranges = ranger.FullNotNullRange()
	}
	hist, cms, err := idxExec.buildStats(ranges, true)
	if err != nil {
		return analyzeResult{Err: err, job: idxExec.job}
	}
	result := analyzeResult{
		TableID: idxExec.tableID,
		Hist:    []*statistics.Histogram{hist},
		Cms:     []*statistics.CMSketch{cms},
		IsIndex: 1,
		job:     idxExec.job,
	}
	result.Count = hist.NullCount
	if hist.Len() > 0 {
		result.Count += hist.Buckets[hist.Len()-1].Count
	}
	return result
}

// AnalyzeIndexExec represents analyze index push down executor.
type AnalyzeIndexExec struct {
	ctx            sessionctx.Context
	tableID        core.AnalyzeTableID
	idxInfo        *model.IndexInfo
	isCommonHandle bool
	concurrency    int
	priority       int
	analyzePB      *tipb.AnalyzeReq
	result         distsql.SelectResult
	countNullRes   distsql.SelectResult
	opts           map[ast.AnalyzeOptionType]uint64
	job            *statistics.AnalyzeJob
}

// fetchAnalyzeResult builds and dispatches the `kv.Request` from given ranges, and stores the `SelectResult`
// in corresponding fields based on the input `isNullRange` argument, which indicates if the range is the
// special null range for single-column index to get the null count.
func (e *AnalyzeIndexExec) fetchAnalyzeResult(ranges []*ranger.Range, isNullRange bool) error {
	var builder distsql.RequestBuilder
	var kvReqBuilder *distsql.RequestBuilder
	if e.isCommonHandle && e.idxInfo.Primary {
		kvReqBuilder = builder.SetCommonHandleRanges(e.ctx.GetSessionVars().StmtCtx, e.tableID.CollectIDs[0], ranges)
	} else {
		kvReqBuilder = builder.SetIndexRanges(e.ctx.GetSessionVars().StmtCtx, e.tableID.CollectIDs[0], e.idxInfo.ID, ranges)
	}
	kvReq, err := kvReqBuilder.
		SetAnalyzeRequest(e.analyzePB).
		SetStartTS(math.MaxUint64).
		SetKeepOrder(true).
		SetConcurrency(e.concurrency).
		Build()
	if err != nil {
		return err
	}
	ctx := context.TODO()
	result, err := distsql.Analyze(ctx, e.ctx.GetClient(), kvReq, e.ctx.GetSessionVars().KVVars, e.ctx.GetSessionVars().InRestrictedSQL)
	if err != nil {
		return err
	}
	result.Fetch(ctx)
	if isNullRange {
		e.countNullRes = result
	} else {
		e.result = result
	}
	return nil
}

func (e *AnalyzeIndexExec) open(ranges []*ranger.Range, considerNull bool) error {
	err := e.fetchAnalyzeResult(ranges, false)
	if err != nil {
		return err
	}
	if considerNull && len(e.idxInfo.Columns) == 1 {
		ranges = ranger.NullRange()
		err = e.fetchAnalyzeResult(ranges, true)
		if err != nil {
			return err
		}
	}
	return nil
}

func (e *AnalyzeIndexExec) buildStatsFromResult(result distsql.SelectResult, needCMS bool) (*statistics.Histogram, *statistics.CMSketch, error) {
	failpoint.Inject("buildStatsFromResult", func(val failpoint.Value) {
		if val.(bool) {
			failpoint.Return(nil, nil, errors.New("mock buildStatsFromResult error"))
		}
	})
	hist := &statistics.Histogram{}
	var cms *statistics.CMSketch
	if needCMS {
		cms = statistics.NewCMSketch(int32(e.opts[ast.AnalyzeOptCMSketchDepth]), int32(e.opts[ast.AnalyzeOptCMSketchWidth]))
	}
	for {
		data, err := result.NextRaw(context.TODO())
		if err != nil {
			return nil, nil, err
		}
		if data == nil {
			break
		}
		resp := &tipb.AnalyzeIndexResp{}
		err = resp.Unmarshal(data)
		if err != nil {
			return nil, nil, err
		}
		respHist := statistics.HistogramFromProto(resp.Hist)
		e.job.Update(int64(respHist.TotalRowCount()))
		hist, err = statistics.MergeHistograms(e.ctx.GetSessionVars().StmtCtx, hist, respHist, int(e.opts[ast.AnalyzeOptNumBuckets]))
		if err != nil {
			return nil, nil, err
		}
		if needCMS {
			if resp.Cms == nil {
				logutil.Logger(context.TODO()).Warn("nil CMS in response", zap.String("table", e.idxInfo.Table.O), zap.String("index", e.idxInfo.Name.O))
			} else if err := cms.MergeCMSketch(statistics.CMSketchFromProto(resp.Cms), 0); err != nil {
				return nil, nil, err
			}
		}
	}
	err := hist.ExtractTopN(cms, len(e.idxInfo.Columns), uint32(e.opts[ast.AnalyzeOptNumTopN]))
	if needCMS && cms != nil {
		cms.CalcDefaultValForAnalyze(uint64(hist.NDV))
	}
	return hist, cms, err
}

func (e *AnalyzeIndexExec) buildStats(ranges []*ranger.Range, considerNull bool) (hist *statistics.Histogram, cms *statistics.CMSketch, err error) {
	if err = e.open(ranges, considerNull); err != nil {
		return nil, nil, err
	}
	defer func() {
		err1 := closeAll(e.result, e.countNullRes)
		if err == nil {
			err = err1
		}
	}()
	hist, cms, err = e.buildStatsFromResult(e.result, true)
	if err != nil {
		return nil, nil, err
	}
	if e.countNullRes != nil {
		nullHist, _, err := e.buildStatsFromResult(e.countNullRes, false)
		if err != nil {
			return nil, nil, err
		}
		if l := nullHist.Len(); l > 0 {
			hist.NullCount = nullHist.Buckets[l-1].Count
		}
	}
	hist.ID = e.idxInfo.ID
	return hist, cms, nil
}

func analyzeColumnsPushdown(colExec *AnalyzeColumnsExec) analyzeResult {
	var ranges []*ranger.Range
	if hc := colExec.handleCols; hc != nil {
		if hc.IsInt() {
			ranges = ranger.FullIntRange(mysql.HasUnsignedFlag(hc.GetCol(0).RetType.Flag))
		} else {
			ranges = ranger.FullNotNullRange()
		}
	} else {
		ranges = ranger.FullIntRange(false)
	}
	hists, cms, extStats, err := colExec.buildStats(ranges, true)
	if err != nil {
		return analyzeResult{Err: err, job: colExec.job}
	}
	result := analyzeResult{
		TableID:  colExec.tableID,
		Hist:     hists,
		Cms:      cms,
		ExtStats: extStats,
		job:      colExec.job,
	}
	hist := hists[0]
	result.Count = hist.NullCount
	if hist.Len() > 0 {
		result.Count += hist.Buckets[hist.Len()-1].Count
	}
	return result
}

// AnalyzeColumnsExec represents Analyze columns push down executor.
type AnalyzeColumnsExec struct {
	ctx           sessionctx.Context
	tableID       core.AnalyzeTableID
	colsInfo      []*model.ColumnInfo
	handleCols    core.HandleCols
	concurrency   int
	priority      int
	analyzePB     *tipb.AnalyzeReq
	resultHandler *tableResultHandler
	opts          map[ast.AnalyzeOptionType]uint64
	job           *statistics.AnalyzeJob
}

func (e *AnalyzeColumnsExec) open(ranges []*ranger.Range) error {
	e.resultHandler = &tableResultHandler{}
	firstPartRanges, secondPartRanges := splitRanges(ranges, true, false)
	firstResult, err := e.buildResp(firstPartRanges)
	if err != nil {
		return err
	}
	if len(secondPartRanges) == 0 {
		e.resultHandler.open(nil, firstResult)
		return nil
	}
	var secondResult distsql.SelectResult
	secondResult, err = e.buildResp(secondPartRanges)
	if err != nil {
		return err
	}
	e.resultHandler.open(firstResult, secondResult)

	return nil
}

func (e *AnalyzeColumnsExec) buildResp(ranges []*ranger.Range) (distsql.SelectResult, error) {
	var builder distsql.RequestBuilder
	var reqBuilder *distsql.RequestBuilder
	if e.handleCols != nil && !e.handleCols.IsInt() {
		reqBuilder = builder.SetCommonHandleRanges(e.ctx.GetSessionVars().StmtCtx, e.tableID.CollectIDs[0], ranges)
	} else {
		reqBuilder = builder.SetTableRanges(e.tableID.CollectIDs[0], ranges, nil)
	}
	// Always set KeepOrder of the request to be true, in order to compute
	// correct `correlation` of columns.
	kvReq, err := reqBuilder.
		SetAnalyzeRequest(e.analyzePB).
		SetStartTS(math.MaxUint64).
		SetKeepOrder(true).
		SetConcurrency(e.concurrency).
		Build()
	if err != nil {
		return nil, err
	}
	ctx := context.TODO()
	result, err := distsql.Analyze(ctx, e.ctx.GetClient(), kvReq, e.ctx.GetSessionVars().KVVars, e.ctx.GetSessionVars().InRestrictedSQL)
	if err != nil {
		return nil, err
	}
	result.Fetch(ctx)
	return result, nil
}

func (e *AnalyzeColumnsExec) buildStats(ranges []*ranger.Range, needExtStats bool) (hists []*statistics.Histogram, cms []*statistics.CMSketch, extStats *statistics.ExtendedStatsColl, err error) {
	if err = e.open(ranges); err != nil {
		return nil, nil, nil, err
	}
	defer func() {
		if err1 := e.resultHandler.Close(); err1 != nil {
			hists = nil
			cms = nil
			extStats = nil
			err = err1
		}
	}()
	pkHist := &statistics.Histogram{}
	collectors := make([]*statistics.SampleCollector, len(e.colsInfo))
	for i := range collectors {
		collectors[i] = &statistics.SampleCollector{
			IsMerger:      true,
			FMSketch:      statistics.NewFMSketch(maxSketchSize),
			MaxSampleSize: int64(e.opts[ast.AnalyzeOptNumSamples]),
			CMSketch:      statistics.NewCMSketch(int32(e.opts[ast.AnalyzeOptCMSketchDepth]), int32(e.opts[ast.AnalyzeOptCMSketchWidth])),
		}
	}
	for {
		data, err1 := e.resultHandler.nextRaw(context.TODO())
		if err1 != nil {
			return nil, nil, nil, err1
		}
		if data == nil {
			break
		}
		resp := &tipb.AnalyzeColumnsResp{}
		err = resp.Unmarshal(data)
		if err != nil {
			return nil, nil, nil, err
		}
		sc := e.ctx.GetSessionVars().StmtCtx
		rowCount := int64(0)
		if hasPkHist(e.handleCols) {
			respHist := statistics.HistogramFromProto(resp.PkHist)
			rowCount = int64(respHist.TotalRowCount())
			pkHist, err = statistics.MergeHistograms(sc, pkHist, respHist, int(e.opts[ast.AnalyzeOptNumBuckets]))
			if err != nil {
				return nil, nil, nil, err
			}
		}
		for i, rc := range resp.Collectors {
			respSample := statistics.SampleCollectorFromProto(rc)
			rowCount = respSample.Count + respSample.NullCount
			collectors[i].MergeSampleCollector(sc, respSample)
		}
		e.job.Update(rowCount)
	}
	timeZone := e.ctx.GetSessionVars().Location()
	if hasPkHist(e.handleCols) {
		pkInfo := e.handleCols.GetCol(0)
		pkHist.ID = pkInfo.ID
		err = pkHist.DecodeTo(pkInfo.RetType, timeZone)
		if err != nil {
			return nil, nil, nil, err
		}
		hists = append(hists, pkHist)
		cms = append(cms, nil)
	}
	for i, col := range e.colsInfo {
		err := collectors[i].ExtractTopN(uint32(e.opts[ast.AnalyzeOptNumTopN]), e.ctx.GetSessionVars().StmtCtx, &col.FieldType, timeZone)
		if err != nil {
			return nil, nil, nil, err
		}
		for j, s := range collectors[i].Samples {
			collectors[i].Samples[j].Ordinal = j
			collectors[i].Samples[j].Value, err = tablecodec.DecodeColumnValue(s.Value.GetBytes(), &col.FieldType, timeZone)
			if err != nil {
				return nil, nil, nil, err
			}
		}
		hg, err := statistics.BuildColumn(e.ctx, int64(e.opts[ast.AnalyzeOptNumBuckets]), col.ID, collectors[i], &col.FieldType)
		if err != nil {
			return nil, nil, nil, err
		}
		hists = append(hists, hg)
		collectors[i].CMSketch.CalcDefaultValForAnalyze(uint64(hg.NDV))
		cms = append(cms, collectors[i].CMSketch)
	}
	if needExtStats {
		statsHandle := domain.GetDomain(e.ctx).StatsHandle()
		extStats, err = statsHandle.BuildExtendedStats(e.tableID.PersistID, e.colsInfo, collectors)
		if err != nil {
			return nil, nil, nil, err
		}
	}
	return hists, cms, extStats, nil
}

func hasPkHist(handleCols core.HandleCols) bool {
	return handleCols != nil && handleCols.IsInt()
}

func pkColsCount(handleCols core.HandleCols) int {
	if handleCols == nil {
		return 0
	}
	return handleCols.NumCols()
}

var (
	fastAnalyzeHistogramSample        = metrics.FastAnalyzeHistogram.WithLabelValues(metrics.LblGeneral, "sample")
	fastAnalyzeHistogramAccessRegions = metrics.FastAnalyzeHistogram.WithLabelValues(metrics.LblGeneral, "access_regions")
	fastAnalyzeHistogramScanKeys      = metrics.FastAnalyzeHistogram.WithLabelValues(metrics.LblGeneral, "scan_keys")
)

func analyzeFastExec(exec *AnalyzeFastExec) []analyzeResult {
	hists, cms, err := exec.buildStats()
	if err != nil {
		return []analyzeResult{{Err: err, job: exec.job}}
	}
	var results []analyzeResult
	pkColCount := pkColsCount(exec.handleCols)
	if len(exec.idxsInfo) > 0 {
		for i := pkColCount + len(exec.colsInfo); i < len(hists); i++ {
			idxResult := analyzeResult{
				TableID: exec.tableID,
				Hist:    []*statistics.Histogram{hists[i]},
				Cms:     []*statistics.CMSketch{cms[i]},
				IsIndex: 1,
				Count:   hists[i].NullCount,
				job:     exec.job,
			}
			if hists[i].Len() > 0 {
				idxResult.Count += hists[i].Buckets[hists[i].Len()-1].Count
			}
			if exec.rowCount != 0 {
				idxResult.Count = exec.rowCount
			}
			results = append(results, idxResult)
		}
	}
	hist := hists[0]
	colResult := analyzeResult{
		TableID: exec.tableID,
		Hist:    hists[:pkColCount+len(exec.colsInfo)],
		Cms:     cms[:pkColCount+len(exec.colsInfo)],
		Count:   hist.NullCount,
		job:     exec.job,
	}
	if hist.Len() > 0 {
		colResult.Count += hist.Buckets[hist.Len()-1].Count
	}
	if exec.rowCount != 0 {
		colResult.Count = exec.rowCount
	}
	results = append(results, colResult)
	return results
}

// AnalyzeFastExec represents Fast Analyze executor.
type AnalyzeFastExec struct {
	ctx         sessionctx.Context
	tableID     core.AnalyzeTableID
	handleCols  core.HandleCols
	colsInfo    []*model.ColumnInfo
	idxsInfo    []*model.IndexInfo
	concurrency int
	opts        map[ast.AnalyzeOptionType]uint64
	tblInfo     *model.TableInfo
	cache       *tikv.RegionCache
	wg          *sync.WaitGroup
	rowCount    int64
	sampCursor  int32
	sampTasks   []*tikv.KeyLocation
	scanTasks   []*tikv.KeyLocation
	collectors  []*statistics.SampleCollector
	randSeed    int64
	job         *statistics.AnalyzeJob
	estSampStep uint32
}

func (e *AnalyzeFastExec) calculateEstimateSampleStep() (err error) {
	sql := fmt.Sprintf("select flag from mysql.stats_histograms where table_id = %d;", e.tableID.PersistID)
	var rows []chunk.Row
	rows, _, err = e.ctx.(sqlexec.RestrictedSQLExecutor).ExecRestrictedSQL(sql)
	if err != nil {
		return
	}
	var historyRowCount uint64
	hasBeenAnalyzed := len(rows) != 0 && rows[0].GetInt64(0) == statistics.AnalyzeFlag
	if hasBeenAnalyzed {
		historyRowCount = uint64(domain.GetDomain(e.ctx).StatsHandle().GetPartitionStats(e.tblInfo, e.tableID.PersistID).Count)
	} else {
		dbInfo, ok := domain.GetDomain(e.ctx).InfoSchema().SchemaByTable(e.tblInfo)
		if !ok {
			err = errors.Errorf("database not found for table '%s'", e.tblInfo.Name)
			return
		}
		var rollbackFn func() error
		rollbackFn, err = e.activateTxnForRowCount()
		if err != nil {
			return
		}
		defer func() {
			if rollbackFn != nil {
				err = rollbackFn()
			}
		}()
		var partition string
		if e.tblInfo.ID != e.tableID.PersistID {
			for _, definition := range e.tblInfo.Partition.Definitions {
				if definition.ID == e.tableID.PersistID {
					partition = fmt.Sprintf(" partition(%s)", definition.Name.L)
					break
				}
			}
		}
		sql := fmt.Sprintf("select count(*) from %s.%s", dbInfo.Name.L, e.tblInfo.Name.L)
		if len(partition) > 0 {
			sql += partition
		}
		var recordSets []sqlexec.RecordSet
		recordSets, err = e.ctx.(sqlexec.SQLExecutor).ExecuteInternal(context.TODO(), sql)
		if err != nil || len(recordSets) == 0 {
			return
		}
		if len(recordSets) == 0 {
			err = errors.Trace(errors.Errorf("empty record set"))
			return
		}
		defer func() {
			for _, r := range recordSets {
				terror.Call(r.Close)
			}
		}()
		chk := recordSets[0].NewChunk()
		err = recordSets[0].Next(context.TODO(), chk)
		if err != nil {
			return
		}
		e.rowCount = chk.GetRow(0).GetInt64(0)
		historyRowCount = uint64(e.rowCount)
	}
	totalSampSize := e.opts[ast.AnalyzeOptNumSamples]
	e.estSampStep = uint32(historyRowCount / totalSampSize)
	return
}

func (e *AnalyzeFastExec) activateTxnForRowCount() (rollbackFn func() error, err error) {
	txn, err := e.ctx.Txn(true)
	if err != nil {
		if kv.ErrInvalidTxn.Equal(err) {
			_, err := e.ctx.(sqlexec.SQLExecutor).ExecuteInternal(context.TODO(), "begin")
			if err != nil {
				return nil, errors.Trace(err)
			}
			rollbackFn = func() error {
				_, err := e.ctx.(sqlexec.SQLExecutor).ExecuteInternal(context.TODO(), "rollback")
				return err
			}
		} else {
			return nil, errors.Trace(err)
		}
	}
	txn.SetOption(kv.Priority, kv.PriorityLow)
	txn.SetOption(kv.IsolationLevel, kv.RC)
	txn.SetOption(kv.NotFillCache, true)
	return nil, nil
}

// buildSampTask build sample tasks.
func (e *AnalyzeFastExec) buildSampTask() (err error) {
	bo := tikv.NewBackofferWithVars(context.Background(), 500, nil)
	store, _ := e.ctx.GetStore().(tikv.Storage)
	e.cache = store.GetRegionCache()
	startKey, endKey := tablecodec.GetTableHandleKeyRange(e.tableID.CollectIDs[0])
	targetKey := startKey
	accessRegionsCounter := 0
	for {
		// Search for the region which contains the targetKey.
		loc, err := e.cache.LocateKey(bo, targetKey)
		if err != nil {
			return err
		}
		if bytes.Compare(endKey, loc.StartKey) < 0 {
			break
		}
		accessRegionsCounter++

		// Set the next search key.
		targetKey = loc.EndKey

		// If the KV pairs in the region all belonging to the table, add it to the sample task.
		if bytes.Compare(startKey, loc.StartKey) <= 0 && len(loc.EndKey) != 0 && bytes.Compare(loc.EndKey, endKey) <= 0 {
			e.sampTasks = append(e.sampTasks, loc)
			continue
		}

		e.scanTasks = append(e.scanTasks, loc)
		if bytes.Compare(loc.StartKey, startKey) < 0 {
			loc.StartKey = startKey
		}
		if bytes.Compare(endKey, loc.EndKey) < 0 || len(loc.EndKey) == 0 {
			loc.EndKey = endKey
			break
		}
	}
	fastAnalyzeHistogramAccessRegions.Observe(float64(accessRegionsCounter))

	return nil
}

func (e *AnalyzeFastExec) decodeValues(handle kv.Handle, sValue []byte, wantCols map[int64]*types.FieldType) (values map[int64]types.Datum, err error) {
	loc := e.ctx.GetSessionVars().Location()
	values, err = tablecodec.DecodeRowToDatumMap(sValue, wantCols, loc)
	if err != nil || e.handleCols == nil {
		return values, err
	}
	wantCols = make(map[int64]*types.FieldType, e.handleCols.NumCols())
	handleColIDs := make([]int64, e.handleCols.NumCols())
	for i := 0; i < e.handleCols.NumCols(); i++ {
		c := e.handleCols.GetCol(i)
		handleColIDs[i] = c.ID
		wantCols[c.ID] = c.RetType
	}
	return tablecodec.DecodeHandleToDatumMap(handle, handleColIDs, wantCols, loc, values)
}

func (e *AnalyzeFastExec) getValueByInfo(colInfo *model.ColumnInfo, values map[int64]types.Datum) (types.Datum, error) {
	val, ok := values[colInfo.ID]
	if !ok {
		return table.GetColOriginDefaultValue(e.ctx, colInfo)
	}
	return val, nil
}

func (e *AnalyzeFastExec) updateCollectorSamples(sValue []byte, sKey kv.Key, samplePos int32) (err error) {
	var handle kv.Handle
	handle, err = tablecodec.DecodeRowKey(sKey)
	if err != nil {
		return err
	}

	// Decode cols for analyze table
	wantCols := make(map[int64]*types.FieldType, len(e.colsInfo))
	for _, col := range e.colsInfo {
		wantCols[col.ID] = &col.FieldType
	}

	// Pre-build index->cols relationship and refill wantCols if not exists(analyze index)
	index2Cols := make([][]*model.ColumnInfo, len(e.idxsInfo))
	for i, idxInfo := range e.idxsInfo {
		for _, idxCol := range idxInfo.Columns {
			colInfo := e.tblInfo.Columns[idxCol.Offset]
			index2Cols[i] = append(index2Cols[i], colInfo)
			wantCols[colInfo.ID] = &colInfo.FieldType
		}
	}

	// Decode the cols value in order.
	var values map[int64]types.Datum
	values, err = e.decodeValues(handle, sValue, wantCols)
	if err != nil {
		return err
	}
	// Update the primary key collector.
	pkColsCount := pkColsCount(e.handleCols)
	for i := 0; i < pkColsCount; i++ {
		col := e.handleCols.GetCol(i)
		v, ok := values[col.ID]
		if !ok {
			return errors.Trace(errors.Errorf("Primary key column not found"))
		}
		if e.collectors[i].Samples[samplePos] == nil {
			e.collectors[i].Samples[samplePos] = &statistics.SampleItem{}
		}
		e.collectors[i].Samples[samplePos].Handle = handle
		e.collectors[i].Samples[samplePos].Value = v
	}

	// Update the columns' collectors.
	for j, colInfo := range e.colsInfo {
		v, err := e.getValueByInfo(colInfo, values)
		if err != nil {
			return err
		}
		if e.collectors[pkColsCount+j].Samples[samplePos] == nil {
			e.collectors[pkColsCount+j].Samples[samplePos] = &statistics.SampleItem{}
		}
		e.collectors[pkColsCount+j].Samples[samplePos].Handle = handle
		e.collectors[pkColsCount+j].Samples[samplePos].Value = v
	}
	// Update the indexes' collectors.
	for j, idxInfo := range e.idxsInfo {
		idxVals := make([]types.Datum, 0, len(idxInfo.Columns))
		cols := index2Cols[j]
		for _, colInfo := range cols {
			v, err := e.getValueByInfo(colInfo, values)
			if err != nil {
				return err
			}
			idxVals = append(idxVals, v)
		}
		var bytes []byte
		bytes, err = codec.EncodeKey(e.ctx.GetSessionVars().StmtCtx, bytes, idxVals...)
		if err != nil {
			return err
		}
		if e.collectors[len(e.colsInfo)+pkColsCount+j].Samples[samplePos] == nil {
			e.collectors[len(e.colsInfo)+pkColsCount+j].Samples[samplePos] = &statistics.SampleItem{}
		}
		e.collectors[len(e.colsInfo)+pkColsCount+j].Samples[samplePos].Handle = handle
		e.collectors[len(e.colsInfo)+pkColsCount+j].Samples[samplePos].Value = types.NewBytesDatum(bytes)
	}
	return nil
}

func (e *AnalyzeFastExec) handleBatchSeekResponse(kvMap map[string][]byte) (err error) {
	length := int32(len(kvMap))
	newCursor := atomic.AddInt32(&e.sampCursor, length)
	samplePos := newCursor - length
	for sKey, sValue := range kvMap {
		exceedNeededSampleCounts := uint64(samplePos) >= e.opts[ast.AnalyzeOptNumSamples]
		if exceedNeededSampleCounts {
			atomic.StoreInt32(&e.sampCursor, int32(e.opts[ast.AnalyzeOptNumSamples]))
			break
		}
		err = e.updateCollectorSamples(sValue, kv.Key(sKey), samplePos)
		if err != nil {
			return err
		}
		samplePos++
	}
	return nil
}

func (e *AnalyzeFastExec) handleScanIter(iter kv.Iterator) (scanKeysSize int, err error) {
	rander := rand.New(rand.NewSource(e.randSeed))
	sampleSize := int64(e.opts[ast.AnalyzeOptNumSamples])
	for ; iter.Valid() && err == nil; err = iter.Next() {
		// reservoir sampling
		scanKeysSize++
		randNum := rander.Int63n(int64(e.sampCursor) + int64(scanKeysSize))
		if randNum > sampleSize && e.sampCursor == int32(sampleSize) {
			continue
		}

		p := rander.Int31n(int32(sampleSize))
		if e.sampCursor < int32(sampleSize) {
			p = e.sampCursor
			e.sampCursor++
		}

		err = e.updateCollectorSamples(iter.Value(), iter.Key(), p)
		if err != nil {
			return
		}
	}
	return
}

func (e *AnalyzeFastExec) handleScanTasks(bo *tikv.Backoffer) (keysSize int, err error) {
	snapshot, err := e.ctx.GetStore().(tikv.Storage).GetSnapshot(kv.MaxVersion)
	if err != nil {
		return 0, err
	}
	if e.ctx.GetSessionVars().GetReplicaRead().IsFollowerRead() {
		snapshot.SetOption(kv.ReplicaRead, kv.ReplicaReadFollower)
	}
	for _, t := range e.scanTasks {
		iter, err := snapshot.Iter(t.StartKey, t.EndKey)
		if err != nil {
			return keysSize, err
		}
		size, err := e.handleScanIter(iter)
		keysSize += size
		if err != nil {
			return keysSize, err
		}
	}
	return keysSize, nil
}

func (e *AnalyzeFastExec) handleSampTasks(workID int, step uint32, err *error) {
	defer e.wg.Done()
	var snapshot kv.Snapshot
	snapshot, *err = e.ctx.GetStore().(tikv.Storage).GetSnapshot(kv.MaxVersion)
	if *err != nil {
		return
	}
	snapshot.SetOption(kv.NotFillCache, true)
	snapshot.SetOption(kv.IsolationLevel, kv.RC)
	snapshot.SetOption(kv.Priority, kv.PriorityLow)
	if e.ctx.GetSessionVars().GetReplicaRead().IsFollowerRead() {
		snapshot.SetOption(kv.ReplicaRead, kv.ReplicaReadFollower)
	}

	rander := rand.New(rand.NewSource(e.randSeed))
	for i := workID; i < len(e.sampTasks); i += e.concurrency {
		task := e.sampTasks[i]
		// randomize the estimate step in range [step - 2 * sqrt(step), step]
		if step > 4 { // 2*sqrt(x) < x
			lower, upper := step-uint32(2*math.Sqrt(float64(step))), step
			step = uint32(rander.Intn(int(upper-lower))) + lower
		}
		snapshot.SetOption(kv.SampleStep, step)
		kvMap := make(map[string][]byte)
		var iter kv.Iterator
		iter, *err = snapshot.Iter(task.StartKey, task.EndKey)
		if *err != nil {
			return
		}
		for iter.Valid() {
			kvMap[string(iter.Key())] = iter.Value()
			*err = iter.Next()
			if *err != nil {
				return
			}
		}
		fastAnalyzeHistogramSample.Observe(float64(len(kvMap)))

		*err = e.handleBatchSeekResponse(kvMap)
		if *err != nil {
			return
		}
	}
}

func (e *AnalyzeFastExec) buildColumnStats(ID int64, collector *statistics.SampleCollector, tp *types.FieldType, rowCount int64) (*statistics.Histogram, *statistics.CMSketch, error) {
	data := make([][]byte, 0, len(collector.Samples))
	for i, sample := range collector.Samples {
		sample.Ordinal = i
		if sample.Value.IsNull() {
			collector.NullCount++
			continue
		}
		bytes, err := tablecodec.EncodeValue(e.ctx.GetSessionVars().StmtCtx, nil, sample.Value)
		if err != nil {
			return nil, nil, err
		}
		data = append(data, bytes)
	}
	// Build CMSketch.
	cmSketch, ndv, scaleRatio := statistics.NewCMSketchWithTopN(int32(e.opts[ast.AnalyzeOptCMSketchDepth]), int32(e.opts[ast.AnalyzeOptCMSketchWidth]), data, uint32(e.opts[ast.AnalyzeOptNumTopN]), uint64(rowCount))
	// Build Histogram.
	hist, err := statistics.BuildColumnHist(e.ctx, int64(e.opts[ast.AnalyzeOptNumBuckets]), ID, collector, tp, rowCount, int64(ndv), collector.NullCount*int64(scaleRatio))
	return hist, cmSketch, err
}

func (e *AnalyzeFastExec) buildIndexStats(idxInfo *model.IndexInfo, collector *statistics.SampleCollector, rowCount int64) (*statistics.Histogram, *statistics.CMSketch, error) {
	data := make([][][]byte, len(idxInfo.Columns))
	for _, sample := range collector.Samples {
		var preLen int
		remained := sample.Value.GetBytes()
		// We need to insert each prefix values into CM Sketch.
		for i := 0; i < len(idxInfo.Columns); i++ {
			var err error
			var value []byte
			value, remained, err = codec.CutOne(remained)
			if err != nil {
				return nil, nil, err
			}
			preLen += len(value)
			data[i] = append(data[i], sample.Value.GetBytes()[:preLen])
		}
	}
	numTop := uint32(e.opts[ast.AnalyzeOptNumTopN])
	cmSketch, ndv, scaleRatio := statistics.NewCMSketchWithTopN(int32(e.opts[ast.AnalyzeOptCMSketchDepth]), int32(e.opts[ast.AnalyzeOptCMSketchWidth]), data[0], numTop, uint64(rowCount))
	// Build CM Sketch for each prefix and merge them into one.
	for i := 1; i < len(idxInfo.Columns); i++ {
		var curCMSketch *statistics.CMSketch
		// `ndv` should be the ndv of full index, so just rewrite it here.
		curCMSketch, ndv, scaleRatio = statistics.NewCMSketchWithTopN(int32(e.opts[ast.AnalyzeOptCMSketchDepth]), int32(e.opts[ast.AnalyzeOptCMSketchWidth]), data[i], numTop, uint64(rowCount))
		err := cmSketch.MergeCMSketch(curCMSketch, numTop)
		if err != nil {
			return nil, nil, err
		}
	}
	// Build Histogram.
	hist, err := statistics.BuildColumnHist(e.ctx, int64(e.opts[ast.AnalyzeOptNumBuckets]), idxInfo.ID, collector, types.NewFieldType(mysql.TypeBlob), rowCount, int64(ndv), collector.NullCount*int64(scaleRatio))
	return hist, cmSketch, err
}

func (e *AnalyzeFastExec) runTasks() ([]*statistics.Histogram, []*statistics.CMSketch, error) {
	errs := make([]error, e.concurrency)
	pkColCount := pkColsCount(e.handleCols)
	// collect column samples and primary key samples and index samples.
	length := len(e.colsInfo) + pkColCount + len(e.idxsInfo)
	e.collectors = make([]*statistics.SampleCollector, length)
	for i := range e.collectors {
		e.collectors[i] = &statistics.SampleCollector{
			MaxSampleSize: int64(e.opts[ast.AnalyzeOptNumSamples]),
			Samples:       make([]*statistics.SampleItem, e.opts[ast.AnalyzeOptNumSamples]),
		}
	}

	e.wg.Add(e.concurrency)
	bo := tikv.NewBackofferWithVars(context.Background(), 500, nil)
	for i := 0; i < e.concurrency; i++ {
		go e.handleSampTasks(i, e.estSampStep, &errs[i])
	}
	e.wg.Wait()
	for _, err := range errs {
		if err != nil {
			return nil, nil, err
		}
	}

	scanKeysSize, err := e.handleScanTasks(bo)
	fastAnalyzeHistogramScanKeys.Observe(float64(scanKeysSize))
	if err != nil {
		return nil, nil, err
	}

	stats := domain.GetDomain(e.ctx).StatsHandle()
	var rowCount int64 = 0
	if stats.Lease() > 0 {
		if t := stats.GetPartitionStats(e.tblInfo, e.tableID.PersistID); !t.Pseudo {
			rowCount = t.Count
		}
	}
	hists, cms := make([]*statistics.Histogram, length), make([]*statistics.CMSketch, length)
	for i := 0; i < length; i++ {
		// Build collector properties.
		collector := e.collectors[i]
		collector.Samples = collector.Samples[:e.sampCursor]
		sort.Slice(collector.Samples, func(i, j int) bool { return collector.Samples[i].Handle.Compare(collector.Samples[j].Handle) < 0 })
		collector.CalcTotalSize()
		// Adjust the row count in case the count of `tblStats` is not accurate and too small.
		rowCount = mathutil.MaxInt64(rowCount, int64(len(collector.Samples)))
		// Scale the total column size.
		if len(collector.Samples) > 0 {
			collector.TotalSize *= rowCount / int64(len(collector.Samples))
		}
		if i < pkColCount {
			pkCol := e.handleCols.GetCol(i)
			hists[i], cms[i], err = e.buildColumnStats(pkCol.ID, e.collectors[i], pkCol.RetType, rowCount)
		} else if i < pkColCount+len(e.colsInfo) {
			hists[i], cms[i], err = e.buildColumnStats(e.colsInfo[i-pkColCount].ID, e.collectors[i], &e.colsInfo[i-pkColCount].FieldType, rowCount)
		} else {
			hists[i], cms[i], err = e.buildIndexStats(e.idxsInfo[i-pkColCount-len(e.colsInfo)], e.collectors[i], rowCount)
		}
		if err != nil {
			return nil, nil, err
		}
	}
	return hists, cms, nil
}

func (e *AnalyzeFastExec) buildStats() (hists []*statistics.Histogram, cms []*statistics.CMSketch, err error) {
	// To set rand seed, it's for unit test.
	// To ensure that random sequences are different in non-test environments, RandSeed must be set time.Now().
	if RandSeed == 1 {
		e.randSeed = time.Now().UnixNano()
	} else {
		e.randSeed = RandSeed
	}

	err = e.buildSampTask()
	if err != nil {
		return nil, nil, err
	}

	return e.runTasks()
}

// AnalyzeTestFastExec is for fast sample in unit test.
type AnalyzeTestFastExec struct {
	AnalyzeFastExec
	Ctx             sessionctx.Context
	PhysicalTableID int64
	HandleCols      core.HandleCols
	ColsInfo        []*model.ColumnInfo
	IdxsInfo        []*model.IndexInfo
	Concurrency     int
	Collectors      []*statistics.SampleCollector
	TblInfo         *model.TableInfo
	Opts            map[ast.AnalyzeOptionType]uint64
}

// TestFastSample only test the fast sample in unit test.
func (e *AnalyzeTestFastExec) TestFastSample() error {
	e.ctx = e.Ctx
	e.handleCols = e.HandleCols
	e.colsInfo = e.ColsInfo
	e.idxsInfo = e.IdxsInfo
	e.concurrency = e.Concurrency
	e.tableID = core.AnalyzeTableID{PersistID: e.PhysicalTableID, CollectIDs: []int64{e.PhysicalTableID}}
	e.wg = &sync.WaitGroup{}
	e.job = &statistics.AnalyzeJob{}
	e.tblInfo = e.TblInfo
	e.opts = e.Opts
	_, _, err := e.buildStats()
	e.Collectors = e.collectors
	return err
}

type analyzeIndexIncrementalExec struct {
	AnalyzeIndexExec
	oldHist *statistics.Histogram
	oldCMS  *statistics.CMSketch
}

func analyzeIndexIncremental(idxExec *analyzeIndexIncrementalExec) analyzeResult {
	startPos := idxExec.oldHist.GetUpper(idxExec.oldHist.Len() - 1)
	values, _, err := codec.DecodeRange(startPos.GetBytes(), len(idxExec.idxInfo.Columns))
	if err != nil {
		return analyzeResult{Err: err, job: idxExec.job}
	}
	ran := ranger.Range{LowVal: values, HighVal: []types.Datum{types.MaxValueDatum()}}
	hist, cms, err := idxExec.buildStats([]*ranger.Range{&ran}, false)
	if err != nil {
		return analyzeResult{Err: err, job: idxExec.job}
	}
	hist, err = statistics.MergeHistograms(idxExec.ctx.GetSessionVars().StmtCtx, idxExec.oldHist, hist, int(idxExec.opts[ast.AnalyzeOptNumBuckets]))
	if err != nil {
		return analyzeResult{Err: err, job: idxExec.job}
	}
	if idxExec.oldCMS != nil && cms != nil {
		err = cms.MergeCMSketch4IncrementalAnalyze(idxExec.oldCMS, uint32(idxExec.opts[ast.AnalyzeOptNumTopN]))
		if err != nil {
			return analyzeResult{Err: err, job: idxExec.job}
		}
		cms.CalcDefaultValForAnalyze(uint64(hist.NDV))
	}
	result := analyzeResult{
		TableID: idxExec.tableID,
		Hist:    []*statistics.Histogram{hist},
		Cms:     []*statistics.CMSketch{cms},
		IsIndex: 1,
		job:     idxExec.job,
	}
	result.Count = hist.NullCount
	if hist.Len() > 0 {
		result.Count += hist.Buckets[hist.Len()-1].Count
	}
	return result
}

type analyzePKIncrementalExec struct {
	AnalyzeColumnsExec
	oldHist *statistics.Histogram
}

func analyzePKIncremental(colExec *analyzePKIncrementalExec) analyzeResult {
	var maxVal types.Datum
	pkInfo := colExec.handleCols.GetCol(0)
	if mysql.HasUnsignedFlag(pkInfo.RetType.Flag) {
		maxVal = types.NewUintDatum(math.MaxUint64)
	} else {
		maxVal = types.NewIntDatum(math.MaxInt64)
	}
	startPos := *colExec.oldHist.GetUpper(colExec.oldHist.Len() - 1)
	ran := ranger.Range{LowVal: []types.Datum{startPos}, LowExclude: true, HighVal: []types.Datum{maxVal}}
	hists, _, _, err := colExec.buildStats([]*ranger.Range{&ran}, false)
	if err != nil {
		return analyzeResult{Err: err, job: colExec.job}
	}
	hist := hists[0]
	hist, err = statistics.MergeHistograms(colExec.ctx.GetSessionVars().StmtCtx, colExec.oldHist, hist, int(colExec.opts[ast.AnalyzeOptNumBuckets]))
	if err != nil {
		return analyzeResult{Err: err, job: colExec.job}
	}
	result := analyzeResult{
		TableID: colExec.tableID,
		Hist:    []*statistics.Histogram{hist},
		Cms:     []*statistics.CMSketch{nil},
		job:     colExec.job,
	}
	if hist.Len() > 0 {
		result.Count += hist.Buckets[hist.Len()-1].Count
	}
	return result
}

// analyzeResult is used to represent analyze result.
type analyzeResult struct {
	TableID  core.AnalyzeTableID
	Hist     []*statistics.Histogram
	Cms      []*statistics.CMSketch
	ExtStats *statistics.ExtendedStatsColl
	Count    int64
	IsIndex  int
	Err      error
	job      *statistics.AnalyzeJob
}