tidb sample 源码
tidb sample 代码
文件路径：/executor/sample.go
// Copyright 2020 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 executor
import (
"context"
"github.com/opentracing/opentracing-go"
"github.com/pingcap/errors"
"github.com/pingcap/tidb/expression"
"github.com/pingcap/tidb/kv"
"github.com/pingcap/tidb/parser/model"
"github.com/pingcap/tidb/sessionctx"
"github.com/pingcap/tidb/table"
"github.com/pingcap/tidb/tablecodec"
"github.com/pingcap/tidb/types"
"github.com/pingcap/tidb/util/chunk"
decoder "github.com/pingcap/tidb/util/rowDecoder"
"github.com/tikv/client-go/v2/tikv"
"golang.org/x/exp/slices"
)
var _ Executor = &TableSampleExecutor{}
// TableSampleExecutor fetches a few rows through kv.Scan
// according to the specific sample method.
type TableSampleExecutor struct {
baseExecutor
table table.Table
startTS uint64
sampler rowSampler
}
// Open initializes necessary variables for using this executor.
func (e *TableSampleExecutor) Open(ctx context.Context) error {
if span := opentracing.SpanFromContext(ctx); span != nil && span.Tracer() != nil {
span1 := span.Tracer().StartSpan("TableSampleExecutor.Open", opentracing.ChildOf(span.Context()))
defer span1.Finish()
}
return nil
}
// Next fills data into the chunk passed by its caller.
// The task was actually done by sampler.
func (e *TableSampleExecutor) Next(ctx context.Context, req *chunk.Chunk) error {
req.Reset()
if e.sampler.finished() {
return nil
}
// TODO(tangenta): add runtime stat & memory tracing
return e.sampler.writeChunk(req)
}
// Close implements the Executor Close interface.
func (e *TableSampleExecutor) Close() error {
return nil
}
type rowSampler interface {
writeChunk(req *chunk.Chunk) error
finished() bool
}
type tableRegionSampler struct {
ctx sessionctx.Context
table table.Table
startTS uint64
partTables []table.PartitionedTable
schema *expression.Schema
fullSchema *expression.Schema
isDesc bool
retTypes []*types.FieldType
rowMap map[int64]types.Datum
restKVRanges []kv.KeyRange
isFinished bool
}
func newTableRegionSampler(ctx sessionctx.Context, t table.Table, startTs uint64, partTables []table.PartitionedTable,
schema *expression.Schema, fullSchema *expression.Schema, retTypes []*types.FieldType, desc bool) *tableRegionSampler {
return &tableRegionSampler{
ctx: ctx,
table: t,
startTS: startTs,
partTables: partTables,
schema: schema,
fullSchema: fullSchema,
isDesc: desc,
retTypes: retTypes,
rowMap: make(map[int64]types.Datum),
}
}
func (s *tableRegionSampler) writeChunk(req *chunk.Chunk) error {
err := s.initRanges()
if err != nil {
return err
}
expectedRowCount := req.RequiredRows()
for expectedRowCount > 0 && len(s.restKVRanges) > 0 {
ranges, err := s.pickRanges(expectedRowCount)
if err != nil {
return err
}
err = s.writeChunkFromRanges(ranges, req)
if err != nil {
return err
}
expectedRowCount = req.RequiredRows() - req.NumRows()
}
if len(s.restKVRanges) == 0 {
s.isFinished = true
}
return nil
}
func (s *tableRegionSampler) initRanges() error {
if s.restKVRanges == nil {
var err error
s.restKVRanges, err = s.splitTableRanges()
if err != nil {
return err
}
sortRanges(s.restKVRanges, s.isDesc)
}
return nil
}
func (s *tableRegionSampler) pickRanges(count int) ([]kv.KeyRange, error) {
var regionKeyRanges []kv.KeyRange
cutPoint := count
if len(s.restKVRanges) < cutPoint {
cutPoint = len(s.restKVRanges)
}
regionKeyRanges, s.restKVRanges = s.restKVRanges[:cutPoint], s.restKVRanges[cutPoint:]
return regionKeyRanges, nil
}
func (s *tableRegionSampler) writeChunkFromRanges(ranges []kv.KeyRange, req *chunk.Chunk) error {
decLoc := s.ctx.GetSessionVars().Location()
cols, decColMap, err := s.buildSampleColAndDecodeColMap()
if err != nil {
return err
}
rowDecoder := decoder.NewRowDecoder(s.table, cols, decColMap)
err = s.scanFirstKVForEachRange(ranges, func(handle kv.Handle, value []byte) error {
_, err := rowDecoder.DecodeAndEvalRowWithMap(s.ctx, handle, value, decLoc, s.rowMap)
if err != nil {
return err
}
currentRow := rowDecoder.CurrentRowWithDefaultVal()
mutRow := chunk.MutRowFromTypes(s.retTypes)
for i, col := range s.schema.Columns {
offset := decColMap[col.ID].Col.Offset
target := currentRow.GetDatum(offset, s.retTypes[i])
mutRow.SetDatum(i, target)
}
req.AppendRow(mutRow.ToRow())
s.resetRowMap()
return nil
})
return err
}
func (s *tableRegionSampler) splitTableRanges() ([]kv.KeyRange, error) {
if len(s.partTables) != 0 {
var ranges []kv.KeyRange
for _, t := range s.partTables {
for _, pid := range t.GetAllPartitionIDs() {
start := tablecodec.GenTableRecordPrefix(pid)
end := start.PrefixNext()
rs, err := splitIntoMultiRanges(s.ctx.GetStore(), start, end)
if err != nil {
return nil, err
}
ranges = append(ranges, rs...)
}
}
return ranges, nil
}
startKey, endKey := s.table.RecordPrefix(), s.table.RecordPrefix().PrefixNext()
return splitIntoMultiRanges(s.ctx.GetStore(), startKey, endKey)
}
func splitIntoMultiRanges(store kv.Storage, startKey, endKey kv.Key) ([]kv.KeyRange, error) {
kvRange := kv.KeyRange{StartKey: startKey, EndKey: endKey}
s, ok := store.(tikv.Storage)
if !ok {
return []kv.KeyRange{kvRange}, nil
}
maxSleep := 10000 // ms
bo := tikv.NewBackofferWithVars(context.Background(), maxSleep, nil)
regions, err := s.GetRegionCache().LoadRegionsInKeyRange(bo, startKey, endKey)
if err != nil {
return nil, errors.Trace(err)
}
var ranges = make([]kv.KeyRange, 0, len(regions))
for _, r := range regions {
start, end := r.StartKey(), r.EndKey()
if kv.Key(start).Cmp(startKey) < 0 {
start = startKey
}
if end == nil || kv.Key(end).Cmp(endKey) > 0 {
end = endKey
}
ranges = append(ranges, kv.KeyRange{StartKey: start, EndKey: end})
}
if len(ranges) == 0 {
return nil, errors.Trace(errors.Errorf("no regions found"))
}
return ranges, nil
}
func sortRanges(ranges []kv.KeyRange, isDesc bool) {
slices.SortFunc(ranges, func(i, j kv.KeyRange) bool {
ir, jr := i.StartKey, j.StartKey
if !isDesc {
return ir.Cmp(jr) < 0
}
return ir.Cmp(jr) > 0
})
}
func (s *tableRegionSampler) buildSampleColAndDecodeColMap() ([]*table.Column, map[int64]decoder.Column, error) {
schemaCols := s.schema.Columns
cols := make([]*table.Column, 0, len(schemaCols))
colMap := make(map[int64]decoder.Column, len(schemaCols))
tableCols := s.table.Cols()
for _, schemaCol := range schemaCols {
for _, tableCol := range tableCols {
if tableCol.ID != schemaCol.ID {
continue
}
// The `MutRow` produced by `DecodeAndEvalRowWithMap` used `ColumnInfo.Offset` as indices.
// To evaluate the columns in virtual generated expression properly,
// indices of column(Column.Index) needs to be resolved against full column's schema.
if schemaCol.VirtualExpr != nil {
var err error
schemaCol.VirtualExpr, err = schemaCol.VirtualExpr.ResolveIndices(s.fullSchema)
if err != nil {
return nil, nil, err
}
}
colMap[tableCol.ID] = decoder.Column{
Col: tableCol,
GenExpr: schemaCol.VirtualExpr,
}
cols = append(cols, tableCol)
}
}
// Schema columns contain _tidb_rowid, append extra handle column info.
if len(cols) < len(schemaCols) && schemaCols[len(schemaCols)-1].ID == model.ExtraHandleID {
extraHandle := model.NewExtraHandleColInfo()
extraHandle.Offset = len(cols)
tableCol := &table.Column{ColumnInfo: extraHandle}
colMap[model.ExtraHandleID] = decoder.Column{
Col: tableCol,
}
cols = append(cols, tableCol)
}
return cols, colMap, nil
}
func (s *tableRegionSampler) scanFirstKVForEachRange(ranges []kv.KeyRange,
fn func(handle kv.Handle, value []byte) error) error {
ver := kv.Version{Ver: s.startTS}
snap := s.ctx.GetStore().GetSnapshot(ver)
setOptionForTopSQL(s.ctx.GetSessionVars().StmtCtx, snap)
concurrency := s.ctx.GetSessionVars().ExecutorConcurrency
if len(ranges) < concurrency {
concurrency = len(ranges)
}
fetchers := make([]*sampleFetcher, concurrency)
for i := 0; i < concurrency; i++ {
fetchers[i] = &sampleFetcher{
workerID: i,
concurrency: concurrency,
kvChan: make(chan *sampleKV),
snapshot: snap,
ranges: ranges,
}
go fetchers[i].run()
}
syncer := sampleSyncer{
fetchers: fetchers,
totalCount: len(ranges),
consumeFn: fn,
}
return syncer.sync()
}
func (s *tableRegionSampler) resetRowMap() {
if s.rowMap == nil {
colLen := len(s.schema.Columns)
s.rowMap = make(map[int64]types.Datum, colLen)
return
}
for id := range s.rowMap {
delete(s.rowMap, id)
}
}
func (s *tableRegionSampler) finished() bool {
return s.isFinished
}
type sampleKV struct {
handle kv.Handle
value []byte
}
type sampleFetcher struct {
workerID int
concurrency int
kvChan chan *sampleKV
err error
snapshot kv.Snapshot
ranges []kv.KeyRange
}
func (s *sampleFetcher) run() {
defer close(s.kvChan)
for i, r := range s.ranges {
if i%s.concurrency != s.workerID {
continue
}
it, err := s.snapshot.Iter(r.StartKey, r.EndKey)
if err != nil {
s.err = err
return
}
hasValue := false
for it.Valid() {
if !tablecodec.IsRecordKey(it.Key()) {
if err = it.Next(); err != nil {
s.err = err
return
}
continue
}
handle, err := tablecodec.DecodeRowKey(it.Key())
if err != nil {
s.err = err
return
}
hasValue = true
s.kvChan <- &sampleKV{handle: handle, value: it.Value()}
break
}
if !hasValue {
s.kvChan <- nil
}
}
}
type sampleSyncer struct {
fetchers []*sampleFetcher
totalCount int
consumeFn func(handle kv.Handle, value []byte) error
}
func (s *sampleSyncer) sync() error {
defer func() {
for _, f := range s.fetchers {
// Cleanup channels to terminate fetcher goroutines.
for _, ok := <-f.kvChan; ok; {
}
}
}()
for i := 0; i < s.totalCount; i++ {
f := s.fetchers[i%len(s.fetchers)]
v, ok := <-f.kvChan
if f.err != nil {
return f.err
}
if ok && v != nil {
err := s.consumeFn(v.handle, v.value)
if err != nil {
return err
}
}
}
return nil
}
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