129 lines
4.6 KiB
Go
129 lines
4.6 KiB
Go
// Copyright 2023 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package pdhelper
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import (
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"context"
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"strconv"
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"strings"
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"sync"
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"time"
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"github.com/jellydator/ttlcache/v3"
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"github.com/pingcap/failpoint"
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"github.com/pingcap/tidb/pkg/kv"
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"github.com/pingcap/tidb/pkg/sessionctx"
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"github.com/pingcap/tidb/pkg/store/helper"
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"github.com/pingcap/tidb/pkg/util"
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"github.com/pingcap/tidb/pkg/util/sqlescape"
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)
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// GlobalPDHelper is the global variable for PDHelper.
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var GlobalPDHelper = defaultPDHelper()
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var globalPDHelperOnce sync.Once
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// PDHelper is used to get some information from PD.
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type PDHelper struct {
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cacheForApproximateTableCountFromStorage *ttlcache.Cache[string, float64]
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getApproximateTableCountFromStorageFunc func(ctx context.Context, sctx sessionctx.Context, tid int64, dbName, tableName, partitionName string) (float64, bool)
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wg util.WaitGroupWrapper
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}
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func defaultPDHelper() *PDHelper {
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cache := ttlcache.New[string, float64](
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ttlcache.WithTTL[string, float64](30*time.Second),
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ttlcache.WithCapacity[string, float64](1024*1024),
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)
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return &PDHelper{
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cacheForApproximateTableCountFromStorage: cache,
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getApproximateTableCountFromStorageFunc: getApproximateTableCountFromStorage,
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}
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}
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// Start is used to start the background task of PDHelper. Currently, the background task is used to clean up TTL cache.
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func (p *PDHelper) Start() {
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globalPDHelperOnce.Do(func() {
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p.wg.Run(p.cacheForApproximateTableCountFromStorage.Start)
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})
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}
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// Stop stops the background task of PDHelper.
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func (p *PDHelper) Stop() {
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p.cacheForApproximateTableCountFromStorage.Stop()
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p.wg.Wait()
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}
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func approximateTableCountKey(tid int64, dbName, tableName, partitionName string) string {
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return strings.Join([]string{strconv.FormatInt(tid, 10), dbName, tableName, partitionName}, "_")
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}
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// GetApproximateTableCountFromStorage gets the approximate count of the table.
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func (p *PDHelper) GetApproximateTableCountFromStorage(
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ctx context.Context, sctx sessionctx.Context,
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tid int64, dbName, tableName, partitionName string,
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) (float64, bool) {
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key := approximateTableCountKey(tid, dbName, tableName, partitionName)
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if item := p.cacheForApproximateTableCountFromStorage.Get(key); item != nil {
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return item.Value(), true
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}
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result, hasPD := p.getApproximateTableCountFromStorageFunc(ctx, sctx, tid, dbName, tableName, partitionName)
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p.cacheForApproximateTableCountFromStorage.Set(key, result, ttlcache.DefaultTTL)
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return result, hasPD
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}
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func getApproximateTableCountFromStorage(
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ctx context.Context, sctx sessionctx.Context,
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tid int64, dbName, tableName, partitionName string,
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) (float64, bool) {
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tikvStore, ok := sctx.GetStore().(helper.Storage)
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if !ok {
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return 0, false
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}
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regionStats, err := helper.NewHelper(tikvStore).GetPDRegionStats(ctx, tid, true)
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failpoint.Inject("calcSampleRateByStorageCount", func() {
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// Force the TiDB thinking that there's PD and the count of region is small.
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err = nil
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regionStats.Count = 1
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// Set a very large approximate count.
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regionStats.StorageKeys = 1000000
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})
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if err != nil {
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return 0, false
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}
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// If this table is not small, we directly use the count from PD,
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// since for a small table, it's possible that it's data is in the same region with part of another large table.
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// Thus, we use the number of the regions of the table's table KV to decide whether the table is small.
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if regionStats.Count > 2 {
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return float64(regionStats.StorageKeys), true
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}
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// 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.
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sql := new(strings.Builder)
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sqlescape.MustFormatSQL(sql, "select count(*) from %n.%n", dbName, tableName)
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if partitionName != "" {
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sqlescape.MustFormatSQL(sql, " partition(%n)", partitionName)
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}
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ctx = kv.WithInternalSourceType(ctx, kv.InternalTxnStats)
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rows, _, err := sctx.GetRestrictedSQLExecutor().ExecRestrictedSQL(ctx, nil, sql.String())
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if err != nil {
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return 0, false
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}
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// If the record set is nil, there's something wrong with the execution. The COUNT(*) would always return one row.
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if len(rows) == 0 || rows[0].Len() == 0 {
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return 0, false
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}
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return float64(rows[0].GetInt64(0)), true
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}
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