*: avoid copy in the SortSampleItems (#48683)

ref #47275

pkg/executor/analyze_col.go

@@ -266,7 +266,7 @@ func (e *AnalyzeColumnsExec) buildStats(ranges []*ranger.Range, needExtStats boo
 		if e.StatsVersion < 2 {
 			hg, err = statistics.BuildColumn(e.ctx, int64(e.opts[ast.AnalyzeOptNumBuckets]), col.ID, collectors[i], &col.FieldType)
 		} else {
-			hg, topn, err = statistics.BuildHistAndTopN(e.ctx, int(e.opts[ast.AnalyzeOptNumBuckets]), int(e.opts[ast.AnalyzeOptNumTopN]), col.ID, collectors[i], &col.FieldType, true, nil)
+			hg, topn, err = statistics.BuildHistAndTopN(e.ctx, int(e.opts[ast.AnalyzeOptNumBuckets]), int(e.opts[ast.AnalyzeOptNumTopN]), col.ID, collectors[i], &col.FieldType, true, nil, true)
 			topNs = append(topNs, topn)
 		}
 		if err != nil {

pkg/executor/analyze_col_v2.go

@@ -850,7 +850,7 @@ workLoop:
 					e.memTracker.Release(collector.MemSize)
 				}
 			}
-			hist, topn, err := statistics.BuildHistAndTopN(e.ctx, int(e.opts[ast.AnalyzeOptNumBuckets]), int(e.opts[ast.AnalyzeOptNumTopN]), task.id, collector, task.tp, task.isColumn, e.memTracker)
+			hist, topn, err := statistics.BuildHistAndTopN(e.ctx, int(e.opts[ast.AnalyzeOptNumBuckets]), int(e.opts[ast.AnalyzeOptNumTopN]), task.id, collector, task.tp, task.isColumn, e.memTracker, e.ctx.GetSessionVars().EnableExtendedStats)
 			if err != nil {
 				resultCh <- err
 				releaseCollectorMemory()

pkg/statistics/builder.go

@@ -127,7 +127,7 @@ func BuildColumnHist(ctx sessionctx.Context, numBuckets, id int64, collector *Sa
 	}
 	sc := ctx.GetSessionVars().StmtCtx
 	samples := collector.Samples
-	samples, err := SortSampleItems(sc, samples)
+	err := sortSampleItems(sc, samples)
 	if err != nil {
 		return nil, err
 	}
@@ -241,6 +241,7 @@ func BuildHistAndTopN(
 	tp *types.FieldType,
 	isColumn bool,
 	memTracker *memory.Tracker,
+	needExtStats bool,
 ) (*Histogram, *TopN, error) {
 	bufferedMemSize := int64(0)
 	bufferedReleaseSize := int64(0)
@@ -278,8 +279,15 @@ func BuildHistAndTopN(
 		return NewHistogram(id, ndv, nullCount, 0, tp, 0, collector.TotalSize), nil, nil
 	}
 	sc := ctx.GetSessionVars().StmtCtx
-	samples := collector.Samples
-	samples, err := SortSampleItems(sc, samples)
+	var samples []*SampleItem
+	// if we need to build extended stats, we need to copy the samples to avoid modifying the original samples.
+	if needExtStats {
+		samples = make([]*SampleItem, len(collector.Samples))
+		copy(samples, collector.Samples)
+	} else {
+		samples = collector.Samples
+	}
+	err := sortSampleItems(sc, samples)
 	if err != nil {
 		return nil, nil, err
 	}

pkg/statistics/builder_ext_stats.go

@@ -105,7 +105,7 @@ func fillExtStatsCorrVals(sctx sessionctx.Context, item *ExtendedStatsItem, cols
 	sc := sctx.GetSessionVars().StmtCtx
 
 	var err error
-	samplesX, err = SortSampleItems(sc, samplesX)
+	err = sortSampleItems(sc, samplesX)
 	if err != nil {
 		return nil
 	}
@@ -118,7 +118,9 @@ func fillExtStatsCorrVals(sctx sessionctx.Context, item *ExtendedStatsItem, cols
 		itemY.Ordinal = i
 		samplesYInXOrder = append(samplesYInXOrder, itemY)
 	}
-	samplesYInYOrder, err := SortSampleItems(sc, samplesYInXOrder)
+	samplesYInYOrder := make([]*SampleItem, len(samplesYInXOrder))
+	copy(samplesYInYOrder, samplesYInXOrder)
+	err = sortSampleItems(sc, samplesYInYOrder)
 	if err != nil {
 		return nil
 	}

pkg/statistics/builder_test.go

@@ -72,6 +72,6 @@ func BenchmarkBuildHistAndTopN(b *testing.B) {
 	memoryTracker := memory.NewTracker(10, 1024*1024*1024)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		_, _, _ = BuildHistAndTopN(ctx, 256, 500, 0, collector, filedType, true, memoryTracker)
+		_, _, _ = BuildHistAndTopN(ctx, 256, 500, 0, collector, filedType, true, memoryTracker, false)
 	}
 }

pkg/statistics/main_test.go

@@ -105,10 +105,9 @@ func createTestStatisticsSamples(t *testing.T) *testStatisticsSamples {
 	}
 	sc := stmtctx.NewStmtCtx()
 
-	var err error
-	s.samples, err = SortSampleItems(sc, samples)
+	err := sortSampleItems(sc, samples)
 	require.NoError(t, err)
-
+	s.samples = samples
 	rc := &recordSet{
 		data:   make([]types.Datum, s.count),
 		count:  s.count,

pkg/statistics/sample.go

@@ -61,20 +61,17 @@ func CopySampleItems(items []*SampleItem) []*SampleItem {
 	return n
 }
 
-// SortSampleItems shallow copies and sorts a slice of SampleItem.
-func SortSampleItems(sc *stmtctx.StatementContext, items []*SampleItem) ([]*SampleItem, error) {
-	sortedItems := make([]*SampleItem, len(items))
-	copy(sortedItems, items)
+func sortSampleItems(sc *stmtctx.StatementContext, items []*SampleItem) error {
 	var err error
-	slices.SortStableFunc(sortedItems, func(i, j *SampleItem) int {
+	slices.SortStableFunc(items, func(i, j *SampleItem) int {
 		var cmp int
 		cmp, err = i.Value.Compare(sc.TypeCtx(), &j.Value, collate.GetBinaryCollator())
 		if err != nil {
 			return -1
 		}
 		return cmp
 	})
-	return sortedItems, err
+	return err
 }
 
 // SampleCollector will collect Samples and calculate the count and ndv of an attribute.

pkg/statistics/sample_test.go

@@ -180,7 +180,7 @@ func TestBuildStatsOnRowSample(t *testing.T) {
 		TotalSize: int64(len(data)) * 8,
 	}
 	tp := types.NewFieldType(mysql.TypeLonglong)
-	hist, topN, err := BuildHistAndTopN(ctx, 5, 4, 1, collector, tp, true, nil)
+	hist, topN, err := BuildHistAndTopN(ctx, 5, 4, 1, collector, tp, true, nil, false)
 	require.Nilf(t, err, "%+v", err)
 	topNStr, err := topN.DecodedString(ctx, []byte{tp.GetType()})
 	require.NoError(t, err)

pkg/statistics/statistics_test.go

@@ -537,7 +537,7 @@ func SubTestBuild() func(*testing.T) {
 		count = col.LessRowCount(nil, types.NewIntDatum(1))
 		require.Equal(t, 5, int(count))
 
-		colv2, topnv2, err := BuildHistAndTopN(ctx, int(bucketCount), topNCount, 2, collector, types.NewFieldType(mysql.TypeLonglong), true, nil)
+		colv2, topnv2, err := BuildHistAndTopN(ctx, int(bucketCount), topNCount, 2, collector, types.NewFieldType(mysql.TypeLonglong), true, nil, false)
 		require.NoError(t, err)
 		require.NotNil(t, topnv2.TopN)
 		// The most common one's occurrence is 9990, the second most common one's occurrence is 30.