statistics: add historgram bench for MergePartitionHist2GlobalHist (#46788)

statistics/BUILD.bazel

@@ -75,6 +75,7 @@ go_test(
         "cmsketch_test.go",
         "feedback_test.go",
         "fmsketch_test.go",
+        "histogram_bench_test.go",
         "histogram_test.go",
         "integration_test.go",
         "main_test.go",

statistics/histogram_bench_test.go

@@ -0,0 +1,107 @@
+// Copyright 2023 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,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package statistics
+
+import (
+	"fmt"
+	"math/rand"
+	"testing"
+
+	"github.com/pingcap/tidb/parser/mysql"
+	"github.com/pingcap/tidb/types"
+	"github.com/pingcap/tidb/util/codec"
+	"github.com/pingcap/tidb/util/mock"
+	"github.com/stretchr/testify/require"
+)
+
+const (
+	histogramLen    = 100
+	popedTopNLen    = 100
+	expBucketNumber = 100
+)
+
+func genBucket4TestData(length int) []*bucket4Test {
+	result := make([]*bucket4Test, 0, length)
+	var lower, upper int64
+	for n := 0; n < length; n++ {
+		if n == 0 {
+			lower = 0
+		} else {
+			lower = upper + 1
+		}
+		if n == length-1 {
+			upper = 10000
+		} else {
+			upper = lower + (rand.Int63n(int64(100*(n+1)) - lower))
+		}
+		result = append(result, &bucket4Test{
+			lower:  lower,
+			upper:  upper,
+			count:  rand.Int63n(10000),
+			repeat: rand.Int63n(100),
+			ndv:    rand.Int63n(100),
+		})
+	}
+	return result
+}
+
+func genHist4Bench(t *testing.B, buckets []*bucket4Test, totColSize int64) *Histogram {
+	h := NewHistogram(0, 0, 0, 0, types.NewFieldType(mysql.TypeBlob), len(buckets), totColSize)
+	for _, bucket := range buckets {
+		lower, err := codec.EncodeKey(nil, nil, types.NewIntDatum(bucket.lower))
+		require.NoError(t, err)
+		upper, err := codec.EncodeKey(nil, nil, types.NewIntDatum(bucket.upper))
+		require.NoError(t, err)
+		di, du := types.NewBytesDatum(lower), types.NewBytesDatum(upper)
+		h.AppendBucketWithNDV(&di, &du, bucket.count, bucket.repeat, bucket.ndv)
+	}
+	return h
+}
+
+func benchmarkMergePartitionHist2GlobalHist(b *testing.B, partition int) {
+	ctx := mock.NewContext()
+	sc := ctx.GetSessionVars().StmtCtx
+	hists := make([]*Histogram, 0, partition)
+	for i := 0; i < partition; i++ {
+		buckets := genBucket4TestData(histogramLen)
+		hist := genHist4Bench(b, buckets, histogramLen)
+		hists = append(hists, hist)
+	}
+	poped := make([]TopNMeta, 0, popedTopNLen)
+	for n := 0; n < popedTopNLen; n++ {
+		b, _ := codec.EncodeKey(sc, nil, types.NewIntDatum(rand.Int63n(10000)))
+		tmp := TopNMeta{
+			Encoded: b,
+			Count:   uint64(rand.Int63n(10000)),
+		}
+		poped = append(poped, tmp)
+	}
+	b.StartTimer()
+	MergePartitionHist2GlobalHist(sc, hists, poped, expBucketNumber, true)
+	b.StopTimer()
+}
+
+var benchmarkPartitionSize = []int{1000, 10000, 100000}
+
+// cmd: go test -run=^$ -bench=BenchmarkMergePartitionHist2GlobalHist -benchmem github.com/pingcap/tidb/statistics
+func BenchmarkMergePartitionHist2GlobalHist(b *testing.B) {
+	for _, size := range benchmarkPartitionSize {
+		b.Run(fmt.Sprintf("Size%d", size), func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				benchmarkMergePartitionHist2GlobalHist(b, size)
+			}
+		})
+	}
+}