statistics: improve memory for mergeGlobalStatsTopNByConcurrency (#45993)

close pingcap/tidb#45727

statistics/cmsketch_bench_test.go

@@ -123,10 +123,7 @@ func benchmarkMergeGlobalStatsTopNByConcurrencyWithHists(partitions int, b *test
 		h.Buckets = append(h.Buckets, statistics.Bucket{Repeat: 10, Count: 40})
 		hists = append(hists, h)
 	}
-	wrapper := &statistics.StatsWrapper{
-		AllTopN: topNs,
-		AllHg:   hists,
-	}
+	wrapper := statistics.NewStatsWrapper(hists, topNs)
 	const mergeConcurrency = 4
 	batchSize := len(wrapper.AllTopN) / mergeConcurrency
 	if batchSize < 1 {

statistics/handle/handle.go

@@ -15,7 +15,6 @@
 package handle
 
 import (
-	"bytes"
 	"context"
 	"encoding/json"
 	"fmt"
@@ -948,19 +947,15 @@ func MergeGlobalStatsTopNByConcurrency(mergeConcurrency, mergeBatchSize int, wra
 
 	// handle Error
 	hasErr := false
+	errMsg := make([]string, 0)
 	for resp := range respCh {
 		if resp.Err != nil {
 			hasErr = true
+			errMsg = append(errMsg, resp.Err.Error())
 		}
 		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, ","))
 	}
 
@@ -972,16 +967,6 @@ func MergeGlobalStatsTopNByConcurrency(mergeConcurrency, mergeBatchSize int, wra
 			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) int {
-					return bytes.Compare(i.Encoded, j.Encoded)
-				})
-				wrapper.AllHg[i].RemoveVals(tmp)
-			}
-		}
 	}
 
 	globalTopN, popedTopn := statistics.GetMergedTopNFromSortedSlice(sorted, n)

statistics/merge_worker.go

@@ -15,6 +15,7 @@
 package statistics
 
 import (
+	"sync"
 	"sync/atomic"
 	"time"
 
@@ -44,6 +45,8 @@ type topnStatsMergeWorker struct {
 	respCh chan<- *TopnStatsMergeResponse
 	// the stats in the wrapper should only be read during the worker
 	statsWrapper *StatsWrapper
+	// shardMutex is used to protect `statsWrapper.AllHg`
+	shardMutex []sync.Mutex
 }
 
 // NewTopnStatsMergeWorker returns topn merge worker
@@ -57,6 +60,7 @@ func NewTopnStatsMergeWorker(
 		respCh: respCh,
 	}
 	worker.statsWrapper = wrapper
+	worker.shardMutex = make([]sync.Mutex, len(wrapper.AllHg))
 	worker.killed = killed
 	return worker
 }
@@ -77,10 +81,9 @@ func NewTopnStatsMergeTask(start, end int) *TopnStatsMergeTask {
 
 // TopnStatsMergeResponse indicates topn merge worker response
 type TopnStatsMergeResponse struct {
-	Err        error
-	TopN       *TopN
-	PopedTopn  []TopNMeta
-	RemoveVals [][]TopNMeta
+	Err       error
+	TopN      *TopN
+	PopedTopn []TopNMeta
 }
 
 // Run runs topn merge like statistics.MergePartTopN2GlobalTopN
@@ -99,7 +102,6 @@ func (worker *topnStatsMergeWorker) Run(timeZone *time.Location, isIndex bool,
 			return
 		}
 		partNum := len(allTopNs)
-		removeVals := make([][]TopNMeta, partNum)
 		// Different TopN structures may hold the same value, we have to merge them.
 		counter := make(map[hack.MutableString]float64)
 		// datumMap is used to store the mapping from the string type to datum type.
@@ -168,13 +170,13 @@ func (worker *topnStatsMergeWorker) Run(timeZone *time.Location, isIndex bool,
 					if count != 0 {
 						counter[encodedVal] += count
 						// Remove the value corresponding to encodedVal from the histogram.
-						removeVals[j] = append(removeVals[j], TopNMeta{Encoded: datum.GetBytes(), Count: uint64(count)})
+						worker.shardMutex[j].Lock()
+						worker.statsWrapper.AllHg[j].BinarySearchRemoveVal(TopNMeta{Encoded: datum.GetBytes(), Count: uint64(count)})
+						worker.shardMutex[j].Unlock()
 					}
 				}
 			}
 		}
-		// record remove values
-		resp.RemoveVals = removeVals
 
 		numTop := len(counter)
 		if numTop == 0 {