executor: add cache for approximate table count

executor/BUILD.bazel

@@ -123,6 +123,7 @@ go_library(
         "//executor/internal/builder",
         "//executor/internal/exec",
         "//executor/internal/mpp",
+        "//executor/internal/pdhelper",
         "//executor/internal/util",
         "//executor/metrics",
         "//executor/mppcoordmanager",

executor/builder.go

@@ -37,7 +37,7 @@ import (
 	"github.com/pingcap/tidb/executor/aggfuncs"
 	"github.com/pingcap/tidb/executor/internal/builder"
 	"github.com/pingcap/tidb/executor/internal/exec"
-	internalutil "github.com/pingcap/tidb/executor/internal/util"
+	"github.com/pingcap/tidb/executor/internal/pdhelper"
 	executor_metrics "github.com/pingcap/tidb/executor/metrics"
 	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/expression/aggregation"
@@ -2787,7 +2787,7 @@ func (b *executorBuilder) getAdjustedSampleRate(task plannercore.AnalyzeColumnsT
 }
 
 func (b *executorBuilder) getApproximateTableCountFromStorage(tid int64, task plannercore.AnalyzeColumnsTask) (float64, bool) {
-	return internalutil.GetApproximateTableCountFromStorage(b.ctx, tid, task.DBName, task.TableName, task.PartitionName)
+	return pdhelper.GlobalPDHelper.GetApproximateTableCountFromStorage(b.ctx, tid, task.DBName, task.TableName, task.PartitionName)
 }
 
 func (b *executorBuilder) buildAnalyzeColumnsPushdown(task plannercore.AnalyzeColumnsTask, opts map[ast.AnalyzeOptionType]uint64, autoAnalyze string, schemaForVirtualColEval *expression.Schema) *analyzeTask {

executor/executor.go

@@ -35,6 +35,7 @@ import (
 	"github.com/pingcap/tidb/domain"
 	"github.com/pingcap/tidb/domain/infosync"
 	"github.com/pingcap/tidb/executor/internal/exec"
+	"github.com/pingcap/tidb/executor/internal/pdhelper"
 	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/infoschema"
 	"github.com/pingcap/tidb/kv"
@@ -171,6 +172,16 @@ func init() {
 	CheckTableFastBucketSize.Store(1024)
 }
 
+// Start the backend components
+func Start() {
+	pdhelper.GlobalPDHelper.Start()
+}
+
+// Stop the backend components
+func Stop() {
+	pdhelper.GlobalPDHelper.Stop()
+}
+
 // Action panics when storage usage exceeds storage quota.
 func (a *globalPanicOnExceed) Action(t *memory.Tracker) {
 	a.mutex.Lock()

executor/infoschema_reader.go

@@ -37,7 +37,7 @@ import (
 	"github.com/pingcap/tidb/domain/resourcegroup"
 	"github.com/pingcap/tidb/errno"
 	"github.com/pingcap/tidb/executor/internal/exec"
-	internalutil "github.com/pingcap/tidb/executor/internal/util"
+	"github.com/pingcap/tidb/executor/internal/pdhelper"
 	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/infoschema"
 	"github.com/pingcap/tidb/kv"
@@ -2097,7 +2097,7 @@ func getRemainDurationForAnalyzeStatusHelper(
 			}
 		}
 		if tid > 0 && totalCnt == 0 {
-			totalCnt, _ = internalutil.GetApproximateTableCountFromStorage(sctx, tid, dbName, tableName, partitionName)
+			totalCnt, _ = pdhelper.GlobalPDHelper.GetApproximateTableCountFromStorage(sctx, tid, dbName, tableName, partitionName)
 		}
 		RemainingDuration, percentage = calRemainInfoForAnalyzeStatus(ctx, int64(totalCnt), processedRows, duration)
 	}

executor/internal/pdhelper/BUILD.bazel

@@ -0,0 +1,30 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "pdhelper",
+    srcs = ["pd.go"],
+    importpath = "github.com/pingcap/tidb/executor/internal/pdhelper",
+    visibility = ["//executor:__subpackages__"],
+    deps = [
+        "//kv",
+        "//sessionctx",
+        "//store/helper",
+        "//util",
+        "//util/sqlexec",
+        "@com_github_jellydator_ttlcache_v3//:ttlcache",
+        "@com_github_pingcap_failpoint//:failpoint",
+    ],
+)
+
+go_test(
+    name = "pdhelper_test",
+    timeout = "short",
+    srcs = ["pd_test.go"],
+    embed = [":pdhelper"],
+    flaky = True,
+    deps = [
+        "//sessionctx",
+        "@com_github_jellydator_ttlcache_v3//:ttlcache",
+        "@com_github_stretchr_testify//require",
+    ],
+)

executor/internal/pdhelper/pd.go

@@ -0,0 +1,124 @@
+// 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 pdhelper
+
+import (
+	"context"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/jellydator/ttlcache/v3"
+	"github.com/pingcap/failpoint"
+	"github.com/pingcap/tidb/kv"
+	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/store/helper"
+	"github.com/pingcap/tidb/util"
+	"github.com/pingcap/tidb/util/sqlexec"
+)
+
+// GlobalPDHelper is the global variable for PDHelper.
+var GlobalPDHelper = defaultPDHelper()
+var globalPDHelperOnce sync.Once
+
+// PDHelper is used to get some information from PD.
+type PDHelper struct {
+	wg                                       util.WaitGroupWrapper
+	cacheForApproximateTableCountFromStorage *ttlcache.Cache[string, float64]
+
+	getApproximateTableCountFromStorageFunc func(sctx sessionctx.Context, tid int64, dbName, tableName, partitionName string) (float64, bool)
+}
+
+func defaultPDHelper() *PDHelper {
+	cache := ttlcache.New[string, float64](
+		ttlcache.WithTTL[string, float64](30*time.Second),
+		ttlcache.WithCapacity[string, float64](1024*1024),
+	)
+	return &PDHelper{
+		cacheForApproximateTableCountFromStorage: cache,
+		getApproximateTableCountFromStorageFunc:  getApproximateTableCountFromStorage,
+	}
+}
+
+// Start is used to start the background task of PDHelper. Currently, the background task is used to clean up TTL cache.
+func (p *PDHelper) Start() {
+	globalPDHelperOnce.Do(func() {
+		p.wg.Run(p.cacheForApproximateTableCountFromStorage.Start)
+	})
+}
+
+// Stop stops the background task of PDHelper.
+func (p *PDHelper) Stop() {
+	p.cacheForApproximateTableCountFromStorage.Stop()
+	p.wg.Wait()
+}
+
+func approximateTableCountKey(tid int64, dbName, tableName, partitionName string) string {
+	return strings.Join([]string{strconv.FormatInt(tid, 10), dbName, tableName, partitionName}, "_")
+}
+
+// GetApproximateTableCountFromStorage gets the approximate count of the table.
+func (p *PDHelper) GetApproximateTableCountFromStorage(sctx sessionctx.Context, tid int64, dbName, tableName, partitionName string) (float64, bool) {
+	key := approximateTableCountKey(tid, dbName, tableName, partitionName)
+	if item := p.cacheForApproximateTableCountFromStorage.Get(key); item != nil {
+		return item.Value(), true
+	}
+	result, hasPD := p.getApproximateTableCountFromStorageFunc(sctx, tid, dbName, tableName, partitionName)
+	p.cacheForApproximateTableCountFromStorage.Set(key, result, ttlcache.DefaultTTL)
+	return result, hasPD
+}
+
+func getApproximateTableCountFromStorage(sctx sessionctx.Context, tid int64, dbName, tableName, partitionName string) (float64, bool) {
+	tikvStore, ok := sctx.GetStore().(helper.Storage)
+	if !ok {
+		return 0, false
+	}
+	regionStats := &helper.PDRegionStats{}
+	pdHelper := helper.NewHelper(tikvStore)
+	err := pdHelper.GetPDRegionStats(tid, regionStats, true)
+	failpoint.Inject("calcSampleRateByStorageCount", func() {
+		// Force the TiDB thinking that there's PD and the count of region is small.
+		err = nil
+		regionStats.Count = 1
+		// Set a very large approximate count.
+		regionStats.StorageKeys = 1000000
+	})
+	if err != nil {
+		return 0, false
+	}
+	// If this table is not small, we directly use the count from PD,
+	// since for a small table, it's possible that it's data is in the same region with part of another large table.
+	// Thus, we use the number of the regions of the table's table KV to decide whether the table is small.
+	if regionStats.Count > 2 {
+		return float64(regionStats.StorageKeys), true
+	}
+	// Otherwise, we use count(*) to calc it's size, since it's very small, the table data can be filled in no more than 2 regions.
+	sql := new(strings.Builder)
+	sqlexec.MustFormatSQL(sql, "select count(*) from %n.%n", dbName, tableName)
+	if partitionName != "" {
+		sqlexec.MustFormatSQL(sql, " partition(%n)", partitionName)
+	}
+	ctx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnStats)
+	rows, _, err := sctx.(sqlexec.RestrictedSQLExecutor).ExecRestrictedSQL(ctx, nil, sql.String())
+	if err != nil {
+		return 0, false
+	}
+	// If the record set is nil, there's something wrong with the execution. The COUNT(*) would always return one row.
+	if len(rows) == 0 || rows[0].Len() == 0 {
+		return 0, false
+	}
+	return float64(rows[0].GetInt64(0)), true
+}

executor/internal/pdhelper/pd_test.go

@@ -0,0 +1,67 @@
+// 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 pdhelper
+
+import (
+	"testing"
+	"time"
+
+	"github.com/jellydator/ttlcache/v3"
+	"github.com/pingcap/tidb/sessionctx"
+	"github.com/stretchr/testify/require"
+)
+
+var globalMockClient mockClient
+
+type mockClient struct {
+	missCnt int
+}
+
+func (m *mockClient) getMissCnt() int {
+	return m.missCnt
+}
+
+func (m *mockClient) getFakeApproximateTableCountFromStorage(_ sessionctx.Context, _ int64, _, _, _ string) (float64, bool) {
+	m.missCnt++
+	return 1.0, true
+}
+
+func TestTTLCache(t *testing.T) {
+	cache := ttlcache.New[string, float64](
+		ttlcache.WithTTL[string, float64](100*time.Millisecond),
+		ttlcache.WithCapacity[string, float64](2),
+	)
+	helper := &PDHelper{
+		cacheForApproximateTableCountFromStorage: cache,
+		getApproximateTableCountFromStorageFunc:  globalMockClient.getFakeApproximateTableCountFromStorage,
+	}
+	helper.GetApproximateTableCountFromStorage(nil, 1, "db", "table", "partition") // Miss
+	require.Equal(t, 1, globalMockClient.getMissCnt())
+	helper.GetApproximateTableCountFromStorage(nil, 1, "db", "table", "partition") // Hit
+	require.Equal(t, 1, globalMockClient.getMissCnt())
+	helper.GetApproximateTableCountFromStorage(nil, 2, "db1", "table1", "partition") // Miss
+	require.Equal(t, 2, globalMockClient.getMissCnt())
+	helper.GetApproximateTableCountFromStorage(nil, 3, "db2", "table2", "partition") // Miss
+	helper.GetApproximateTableCountFromStorage(nil, 1, "db", "table", "partition")   // Miss
+	require.Equal(t, 4, globalMockClient.getMissCnt())
+	helper.GetApproximateTableCountFromStorage(nil, 3, "db2", "table2", "partition") // Hit
+	require.Equal(t, 4, globalMockClient.getMissCnt())
+	time.Sleep(200 * time.Millisecond)
+	// All is miss.
+	helper.GetApproximateTableCountFromStorage(nil, 1, "db", "table", "partition")
+	helper.GetApproximateTableCountFromStorage(nil, 2, "db1", "table1", "partition")
+	helper.GetApproximateTableCountFromStorage(nil, 3, "db2", "table2", "partition")
+	require.Equal(t, 7, globalMockClient.getMissCnt())
+}

executor/internal/util/BUILD.bazel

@@ -9,12 +9,7 @@ go_library(
     importpath = "github.com/pingcap/tidb/executor/internal/util",
     visibility = ["//executor:__subpackages__"],
     deps = [
-        "//kv",
-        "//sessionctx",
-        "//store/helper",
-        "//util/sqlexec",
         "@com_github_pingcap_errors//:errors",
-        "@com_github_pingcap_failpoint//:failpoint",
         "@com_github_pingcap_tipb//go-tipb",
     ],
 )

executor/internal/util/util.go

@@ -13,57 +13,3 @@
 // limitations under the License.
 
 package util
-
-import (
-	"context"
-	"strings"
-
-	"github.com/pingcap/failpoint"
-	"github.com/pingcap/tidb/kv"
-	"github.com/pingcap/tidb/sessionctx"
-	"github.com/pingcap/tidb/store/helper"
-	"github.com/pingcap/tidb/util/sqlexec"
-)
-
-// GetApproximateTableCountFromStorage gets the approximate count of the table.
-func GetApproximateTableCountFromStorage(sctx sessionctx.Context, tid int64, dbName, tableName, partitionName string) (float64, bool) {
-	tikvStore, ok := sctx.GetStore().(helper.Storage)
-	if !ok {
-		return 0, false
-	}
-	regionStats := &helper.PDRegionStats{}
-	pdHelper := helper.NewHelper(tikvStore)
-	err := pdHelper.GetPDRegionStats(tid, regionStats, true)
-	failpoint.Inject("calcSampleRateByStorageCount", func() {
-		// Force the TiDB thinking that there's PD and the count of region is small.
-		err = nil
-		regionStats.Count = 1
-		// Set a very large approximate count.
-		regionStats.StorageKeys = 1000000
-	})
-	if err != nil {
-		return 0, false
-	}
-	// If this table is not small, we directly use the count from PD,
-	// since for a small table, it's possible that it's data is in the same region with part of another large table.
-	// Thus, we use the number of the regions of the table's table KV to decide whether the table is small.
-	if regionStats.Count > 2 {
-		return float64(regionStats.StorageKeys), true
-	}
-	// Otherwise, we use count(*) to calc it's size, since it's very small, the table data can be filled in no more than 2 regions.
-	sql := new(strings.Builder)
-	sqlexec.MustFormatSQL(sql, "select count(*) from %n.%n", dbName, tableName)
-	if partitionName != "" {
-		sqlexec.MustFormatSQL(sql, " partition(%n)", partitionName)
-	}
-	ctx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnStats)
-	rows, _, err := sctx.(sqlexec.RestrictedSQLExecutor).ExecRestrictedSQL(ctx, nil, sql.String())
-	if err != nil {
-		return 0, false
-	}
-	// If the record set is nil, there's something wrong with the execution. The COUNT(*) would always return one row.
-	if len(rows) == 0 || rows[0].Len() == 0 {
-		return 0, false
-	}
-	return float64(rows[0].GetInt64(0)), true
-}

tidb-server/main.go

@@ -235,7 +235,7 @@ func main() {
 	setupMetrics()
 
 	keyspaceName := keyspace.GetKeyspaceNameBySettings()
-
+	executor.Start()
 	resourcemanager.InstanceResourceManager.Start()
 	storage, dom := createStoreAndDomain(keyspaceName)
 	svr := createServer(storage, dom)
@@ -251,6 +251,7 @@ func main() {
 		cleanup(svr, storage, dom)
 		cpuprofile.StopCPUProfiler()
 		resourcemanager.InstanceResourceManager.Stop()
+		executor.Stop()
 		close(exited)
 	})
 	topsql.SetupTopSQL()