statistics: support merge global topn in concurrency

executor/analyze_test.go

@@ -17,6 +17,7 @@ package executor_test
 import (
 	"fmt"
 	"io/ioutil"
+	"strconv"
 	"strings"
 	"sync/atomic"
 	"testing"
@@ -338,3 +339,78 @@ func TestAnalyzePartitionTableForFloat(t *testing.T) {
 	}
 	tk.MustExec("analyze table t1")
 }
+
+func TestAnalyzePartitionTableByConcurrencyInDynamic(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("set @@tidb_partition_prune_mode='dynamic'")
+	tk.MustExec("use test")
+	tk.MustExec("create table t(id int) partition by hash(id) partitions 4")
+	testcases := []struct {
+		concurrency string
+	}{
+		{
+			concurrency: "1",
+		},
+		{
+			concurrency: "2",
+		},
+		{
+			concurrency: "3",
+		},
+		{
+			concurrency: "4",
+		},
+		{
+			concurrency: "5",
+		},
+	}
+	// assert empty table
+	for _, tc := range testcases {
+		concurrency := tc.concurrency
+		fmt.Println("testcase ", concurrency)
+		tk.MustExec(fmt.Sprintf("set @@tidb_merge_partition_stats_concurrency=%v", concurrency))
+		tk.MustQuery("select @@tidb_merge_partition_stats_concurrency").Check(testkit.Rows(concurrency))
+		tk.MustExec("analyze table t")
+		tk.MustQuery("show stats_topn where partition_name = 'global' and table_name = 't'")
+	}
+
+	for i := 1; i <= 500; i++ {
+		for j := 1; j <= 20; j++ {
+			tk.MustExec(fmt.Sprintf("insert into t (id) values (%v)", j))
+		}
+	}
+	var expected [][]interface{}
+	for i := 1; i <= 20; i++ {
+		expected = append(expected, []interface{}{
+			strconv.FormatInt(int64(i), 10), "500",
+		})
+	}
+	testcases = []struct {
+		concurrency string
+	}{
+		{
+			concurrency: "1",
+		},
+		{
+			concurrency: "2",
+		},
+		{
+			concurrency: "3",
+		},
+		{
+			concurrency: "4",
+		},
+		{
+			concurrency: "5",
+		},
+	}
+	for _, tc := range testcases {
+		concurrency := tc.concurrency
+		fmt.Println("testcase ", concurrency)
+		tk.MustExec(fmt.Sprintf("set @@tidb_merge_partition_stats_concurrency=%v", concurrency))
+		tk.MustQuery("select @@tidb_merge_partition_stats_concurrency").Check(testkit.Rows(concurrency))
+		tk.MustExec("analyze table t")
+		tk.MustQuery("show stats_topn where partition_name = 'global' and table_name = 't'").CheckAt([]int{5, 6}, expected)
+	}
+}

sessionctx/variable/session.go

@@ -1271,6 +1271,9 @@ type SessionVars struct {
 	// LastPlanReplayerToken indicates the last plan replayer token
 	LastPlanReplayerToken string
 
+	// AnalyzePartitionMergeConcurrency indicates concurrency for merging partition stats
+	AnalyzePartitionMergeConcurrency int
+
 	HookContext
 }
 

sessionctx/variable/sysvar.go

@@ -1916,6 +1916,13 @@ var defaultSysVars = []*SysVar{
 		s.RangeMaxSize = TidbOptInt64(val, DefTiDBOptRangeMaxSize)
 		return nil
 	}},
+	{
+		Scope: ScopeGlobal | ScopeSession, Name: TiDBMergePartitionStatsConcurrency, Value: strconv.FormatInt(DefTiDBMergePartitionStatsConcurrency, 10), Type: TypeInt, MinValue: 1, MaxValue: 32,
+		SetSession: func(s *SessionVars, val string) error {
+			s.AnalyzePartitionMergeConcurrency = TidbOptInt(val, DefTiDBMergePartitionStatsConcurrency)
+			return nil
+		},
+	},
 }
 
 // FeedbackProbability points to the FeedbackProbability in statistics package.

sessionctx/variable/tidb_vars.go

@@ -749,6 +749,9 @@ const (
 	// ranges would exceed the limit, it chooses less accurate ranges such as full range. 0 indicates that there is no memory
 	// limit for ranges.
 	TiDBOptRangeMaxSize = "tidb_opt_range_max_size"
+
+	// TiDBMergePartitionStatsConcurrency indicates the concurrecny when merge partition stats into global stats
+	TiDBMergePartitionStatsConcurrency = "tidb_merge_partition_stats_concurrency"
 )
 
 // TiDB vars that have only global scope
@@ -1057,6 +1060,7 @@ const (
 	DefTiDBOptRangeMaxSize                          = 0
 	DefTiDBCostModelVer                             = 1
 	DefTiDBServerMemoryLimitSessMinSize             = 128 << 20
+	DefTiDBMergePartitionStatsConcurrency           = 1
 	DefTiDBServerMemoryLimitGCTrigger               = 0.7
 	DefTiDBEnableGOGCTuner                          = true
 )

statistics/cmsketch.go

@@ -21,6 +21,7 @@ import (
 	"reflect"
 	"sort"
 	"strings"
+	"time"
 
 	"github.com/pingcap/errors"
 	"github.com/pingcap/failpoint"
@@ -729,7 +730,7 @@ func NewTopN(n int) *TopN {
 //  1. `*TopN` is the final global-level topN.
 //  2. `[]TopNMeta` is the left topN value from the partition-level TopNs, but is not placed to global-level TopN. We should put them back to histogram latter.
 //  3. `[]*Histogram` are the partition-level histograms which just delete some values when we merge the global-level topN.
-func MergePartTopN2GlobalTopN(sc *stmtctx.StatementContext, version int, topNs []*TopN, n uint32, hists []*Histogram, isIndex bool) (*TopN, []TopNMeta, []*Histogram, error) {
+func MergePartTopN2GlobalTopN(loc *time.Location, version int, topNs []*TopN, n uint32, hists []*Histogram, isIndex bool) (*TopN, []TopNMeta, []*Histogram, error) {
 	if checkEmptyTopNs(topNs) {
 		return nil, nil, hists, nil
 	}
@@ -781,7 +782,7 @@ func MergePartTopN2GlobalTopN(sc *stmtctx.StatementContext, version int, topNs [
 						var err error
 						if types.IsTypeTime(hists[0].Tp.GetType()) {
 							// handle datetime values specially since they are encoded to int and we'll get int values if using DecodeOne.
-							_, d, err = codec.DecodeAsDateTime(val.Encoded, hists[0].Tp.GetType(), sc.TimeZone)
+							_, d, err = codec.DecodeAsDateTime(val.Encoded, hists[0].Tp.GetType(), loc)
 						} else if types.IsTypeFloat(hists[0].Tp.GetType()) {
 							_, d, err = codec.DecodeAsFloat32(val.Encoded, hists[0].Tp.GetType())
 						} else {
@@ -866,6 +867,22 @@ func checkEmptyTopNs(topNs []*TopN) bool {
 	return count == 0
 }
 
+// SortTopnMeta sort topnMeta
+func SortTopnMeta(topnMetas []TopNMeta) []TopNMeta {
+	slices.SortFunc(topnMetas, func(i, j TopNMeta) bool {
+		if i.Count != j.Count {
+			return i.Count > j.Count
+		}
+		return bytes.Compare(i.Encoded, j.Encoded) < 0
+	})
+	return topnMetas
+}
+
+// GetMergedTopNFromSortedSlice returns merged topn
+func GetMergedTopNFromSortedSlice(sorted []TopNMeta, n uint32) (*TopN, []TopNMeta) {
+	return getMergedTopNFromSortedSlice(sorted, n)
+}
+
 func getMergedTopNFromSortedSlice(sorted []TopNMeta, n uint32) (*TopN, []TopNMeta) {
 	slices.SortFunc(sorted, func(i, j TopNMeta) bool {
 		if i.Count != j.Count {

statistics/handle/handle.go

@@ -15,6 +15,7 @@
 package handle
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -56,6 +57,9 @@ import (
 const (
 	// TiDBGlobalStats represents the global-stats for a partitioned table.
 	TiDBGlobalStats = "global"
+
+	// maxPartitionMergeBatchSize indicates the max batch size for a worker to merge partition stats
+	maxPartitionMergeBatchSize = 256
 )
 
 // Handle can update stats info periodically.
@@ -547,7 +551,8 @@ func (h *Handle) mergePartitionStats2GlobalStats(sc sessionctx.Context,
 		// Because after merging TopN, some numbers will be left.
 		// These remaining topN numbers will be used as a separate bucket for later histogram merging.
 		var popedTopN []statistics.TopNMeta
-		globalStats.TopN[i], popedTopN, allHg[i], err = statistics.MergePartTopN2GlobalTopN(sc.GetSessionVars().StmtCtx, sc.GetSessionVars().AnalyzeVersion, allTopN[i], uint32(opts[ast.AnalyzeOptNumTopN]), allHg[i], isIndex == 1)
+		wrapper := statistics.NewStatsWrapper(allHg[i], allTopN[i])
+		globalStats.TopN[i], popedTopN, allHg[i], err = h.mergeGlobalStatsTopN(sc, wrapper, sc.GetSessionVars().StmtCtx.TimeZone, sc.GetSessionVars().AnalyzeVersion, uint32(opts[ast.AnalyzeOptNumTopN]), isIndex == 1)
 		if err != nil {
 			return
 		}
@@ -579,6 +584,103 @@ func (h *Handle) mergePartitionStats2GlobalStats(sc sessionctx.Context,
 	return
 }
 
+func (h *Handle) mergeGlobalStatsTopN(sc sessionctx.Context, wrapper *statistics.StatsWrapper,
+	timeZone *time.Location, version int, n uint32, isIndex bool) (*statistics.TopN,
+	[]statistics.TopNMeta, []*statistics.Histogram, error) {
+	mergeConcurrency := sc.GetSessionVars().AnalyzePartitionMergeConcurrency
+	// use original method if concurrency equals 1 or for version1
+	if mergeConcurrency < 2 {
+		return statistics.MergePartTopN2GlobalTopN(timeZone, version, wrapper.AllTopN, n, wrapper.AllHg, isIndex)
+	}
+	batchSize := len(wrapper.AllTopN) / mergeConcurrency
+	if batchSize < 1 {
+		batchSize = 1
+	} else if batchSize > maxPartitionMergeBatchSize {
+		batchSize = maxPartitionMergeBatchSize
+	}
+	return h.mergeGlobalStatsTopNByConcurrency(mergeConcurrency, batchSize, wrapper, timeZone, version, n, isIndex)
+}
+
+// mergeGlobalStatsTopNByConcurrency merge partition topN by concurrency
+// To merge global stats topn by concurrency, we will separate the partition topn in concurrency part and deal it with different worker.
+// mergeConcurrency is used to control the total concurrency of the running worker, and mergeBatchSize is sued to control
+// the partition size for each worker to solve it
+func (h *Handle) mergeGlobalStatsTopNByConcurrency(mergeConcurrency, mergeBatchSize int, wrapper *statistics.StatsWrapper,
+	timeZone *time.Location, version int, n uint32, isIndex bool) (*statistics.TopN,
+	[]statistics.TopNMeta, []*statistics.Histogram, error) {
+	if len(wrapper.AllTopN) < mergeConcurrency {
+		mergeConcurrency = len(wrapper.AllTopN)
+	}
+	tasks := make([]*statistics.TopnStatsMergeTask, 0)
+	for start := 0; start < len(wrapper.AllTopN); {
+		end := start + mergeBatchSize
+		if end > len(wrapper.AllTopN) {
+			end = len(wrapper.AllTopN)
+		}
+		task := statistics.NewTopnStatsMergeTask(start, end)
+		tasks = append(tasks, task)
+		start = end
+	}
+	taskNum := len(tasks)
+	wg := &sync.WaitGroup{}
+	taskCh := make(chan *statistics.TopnStatsMergeTask, taskNum)
+	respCh := make(chan *statistics.TopnStatsMergeResponse, taskNum)
+	wg.Add(mergeConcurrency)
+	for i := 0; i < mergeConcurrency; i++ {
+		worker := statistics.NewTopnStatsMergeWorker(wg, taskCh, respCh, wrapper)
+		go worker.Run(timeZone, isIndex, n, version)
+	}
+	for _, task := range tasks {
+		taskCh <- task
+	}
+	close(taskCh)
+	wg.Wait()
+	close(respCh)
+	resps := make([]*statistics.TopnStatsMergeResponse, 0)
+
+	// handle Error
+	hasErr := false
+	for resp := range respCh {
+		if resp.Err != nil {
+			hasErr = true
+		}
+		resps = append(resps, resp)
+	}
+	if hasErr {
+		errMsg := make([]string, 0)
+		for _, resp := range resps {
+			if resp.Err != nil {
+				errMsg = append(errMsg, resp.Err.Error())
+			}
+		}
+		return nil, nil, nil, errors.New(strings.Join(errMsg, ","))
+	}
+
+	// fetch the response from each worker and merge them into global topn stats
+	sorted := make([]statistics.TopNMeta, 0, mergeConcurrency)
+	leftTopn := make([]statistics.TopNMeta, 0)
+	for _, resp := range resps {
+		if resp.TopN != nil {
+			sorted = append(sorted, resp.TopN.TopN...)
+		}
+		leftTopn = append(leftTopn, resp.PopedTopn...)
+		for i, removeTopn := range resp.RemoveVals {
+			// Remove the value from the Hists.
+			if len(removeTopn) > 0 {
+				tmp := removeTopn
+				slices.SortFunc(tmp, func(i, j statistics.TopNMeta) bool {
+					cmpResult := bytes.Compare(i.Encoded, j.Encoded)
+					return cmpResult < 0
+				})
+				wrapper.AllHg[i].RemoveVals(tmp)
+			}
+		}
+	}
+
+	globalTopN, popedTopn := statistics.GetMergedTopNFromSortedSlice(sorted, n)
+	return globalTopN, statistics.SortTopnMeta(append(leftTopn, popedTopn...)), wrapper.AllHg, nil
+}
+
 func (h *Handle) getTableByPhysicalID(is infoschema.InfoSchema, physicalID int64) (table.Table, bool) {
 	if is.SchemaMetaVersion() != h.mu.schemaVersion {
 		h.mu.schemaVersion = is.SchemaMetaVersion()