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executor: add cache for approximate table count (pingcap#44979)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,30 @@ | ||
| load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test") | ||
|
|
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| 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", | ||
| ], | ||
| ) |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -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. | ||
|
|
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| package pdhelper | ||
|
|
||
| import ( | ||
| "context" | ||
| "strconv" | ||
| "strings" | ||
| "sync" | ||
| "time" | ||
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|
||
| "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 | ||
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| // PDHelper is used to get some information from PD. | ||
| type PDHelper struct { | ||
| wg util.WaitGroupWrapper | ||
| cacheForApproximateTableCountFromStorage *ttlcache.Cache[string, float64] | ||
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| getApproximateTableCountFromStorageFunc func(sctx sessionctx.Context, tid int64, dbName, tableName, partitionName string) (float64, bool) | ||
| } | ||
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|
||
| 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) | ||
| }) | ||
| } | ||
|
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| // Stop stops the background task of PDHelper. | ||
| func (p *PDHelper) Stop() { | ||
| p.cacheForApproximateTableCountFromStorage.Stop() | ||
| p.wg.Wait() | ||
| } | ||
|
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||
| func approximateTableCountKey(tid int64, dbName, tableName, partitionName string) string { | ||
| return strings.Join([]string{strconv.FormatInt(tid, 10), dbName, tableName, partitionName}, "_") | ||
| } | ||
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| // 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 | ||
| } | ||
|
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||
| 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 | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -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" | ||
|
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| "github.com/jellydator/ttlcache/v3" | ||
| "github.com/pingcap/tidb/sessionctx" | ||
| "github.com/stretchr/testify/require" | ||
| ) | ||
|
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| var globalMockClient mockClient | ||
|
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| type mockClient struct { | ||
| missCnt int | ||
| } | ||
|
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| func (m *mockClient) getMissCnt() int { | ||
| return m.missCnt | ||
| } | ||
|
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| func (m *mockClient) getFakeApproximateTableCountFromStorage(_ sessionctx.Context, _ int64, _, _, _ string) (float64, bool) { | ||
| m.missCnt++ | ||
| return 1.0, true | ||
| } | ||
|
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| 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()) | ||
| } |
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