70 lines
2.6 KiB
Go
70 lines
2.6 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 util
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import (
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"context"
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"strings"
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"github.com/pingcap/failpoint"
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"github.com/pingcap/tidb/kv"
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"github.com/pingcap/tidb/sessionctx"
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"github.com/pingcap/tidb/store/helper"
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"github.com/pingcap/tidb/util/sqlexec"
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)
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// GetApproximateTableCountFromStorage gets the approximate count of the table.
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func GetApproximateTableCountFromStorage(sctx sessionctx.Context, tid int64, dbName, tableName, partitionName string) (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 := &helper.PDRegionStats{}
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pdHelper := helper.NewHelper(tikvStore)
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err := pdHelper.GetPDRegionStats(tid, regionStats, 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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sqlexec.MustFormatSQL(sql, "select count(*) from %n.%n", dbName, tableName)
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if partitionName != "" {
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sqlexec.MustFormatSQL(sql, " partition(%n)", partitionName)
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}
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ctx := kv.WithInternalSourceType(context.Background(), kv.InternalTxnStats)
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rows, _, err := sctx.(sqlexec.RestrictedSQLExecutor).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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