tidb sort 源码
tidb sort 代码
文件路径：/executor/sort.go
// Copyright 2017 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 (
"container/heap"
"context"
"errors"
"github.com/pingcap/failpoint"
"github.com/pingcap/tidb/expression"
plannercore "github.com/pingcap/tidb/planner/core"
"github.com/pingcap/tidb/planner/util"
"github.com/pingcap/tidb/sessionctx/variable"
"github.com/pingcap/tidb/util/chunk"
"github.com/pingcap/tidb/util/disk"
"github.com/pingcap/tidb/util/mathutil"
"github.com/pingcap/tidb/util/memory"
"golang.org/x/exp/slices"
)
// SortExec represents sorting executor.
type SortExec struct {
baseExecutor
ByItems []*util.ByItems
Idx int
fetched bool
schema *expression.Schema
// keyColumns is the column index of the by items.
keyColumns []int
// keyCmpFuncs is used to compare each ByItem.
keyCmpFuncs []chunk.CompareFunc
// rowChunks is the chunks to store row values.
rowChunks *chunk.SortedRowContainer
memTracker *memory.Tracker
diskTracker *disk.Tracker
// partitionList is the chunks to store row values for partitions. Every partition is a sorted list.
partitionList []*chunk.SortedRowContainer
// multiWayMerge uses multi-way merge for spill disk.
// The multi-way merge algorithm can refer to https://en.wikipedia.org/wiki/K-way_merge_algorithm
multiWayMerge *multiWayMerge
// spillAction save the Action for spill disk.
spillAction *chunk.SortAndSpillDiskAction
}
// Close implements the Executor Close interface.
func (e *SortExec) Close() error {
for _, container := range e.partitionList {
err := container.Close()
if err != nil {
return err
}
}
e.partitionList = e.partitionList[:0]
if e.rowChunks != nil {
e.memTracker.Consume(-e.rowChunks.GetMemTracker().BytesConsumed())
e.rowChunks = nil
}
e.memTracker = nil
e.diskTracker = nil
e.multiWayMerge = nil
if e.spillAction != nil {
e.spillAction.SetFinished()
}
e.spillAction = nil
return e.children[0].Close()
}
// Open implements the Executor Open interface.
func (e *SortExec) Open(ctx context.Context) error {
e.fetched = false
e.Idx = 0
// To avoid duplicated initialization for TopNExec.
if e.memTracker == nil {
e.memTracker = memory.NewTracker(e.id, -1)
e.memTracker.AttachTo(e.ctx.GetSessionVars().StmtCtx.MemTracker)
e.diskTracker = memory.NewTracker(e.id, -1)
e.diskTracker.AttachTo(e.ctx.GetSessionVars().StmtCtx.DiskTracker)
}
e.partitionList = e.partitionList[:0]
return e.children[0].Open(ctx)
}
// Next implements the Executor Next interface.
// Sort constructs the result following these step:
// 1. Read as mush as rows into memory.
// 2. If memory quota is triggered, sort these rows in memory and put them into disk as partition 1, then reset
// the memory quota trigger and return to step 1
// 3. If memory quota is not triggered and child is consumed, sort these rows in memory as partition N.
// 4. Merge sort if the count of partitions is larger than 1. If there is only one partition in step 4, it works
// just like in-memory sort before.
func (e *SortExec) Next(ctx context.Context, req *chunk.Chunk) error {
req.Reset()
if !e.fetched {
e.initCompareFuncs()
e.buildKeyColumns()
err := e.fetchRowChunks(ctx)
if err != nil {
return err
}
e.fetched = true
}
if len(e.partitionList) == 0 {
return nil
}
if len(e.partitionList) > 1 {
if err := e.externalSorting(req); err != nil {
return err
}
} else {
for !req.IsFull() && e.Idx < e.partitionList[0].NumRow() {
row, err := e.partitionList[0].GetSortedRow(e.Idx)
if err != nil {
return err
}
req.AppendRow(row)
e.Idx++
}
}
return nil
}
func (e *SortExec) externalSorting(req *chunk.Chunk) (err error) {
if e.multiWayMerge == nil {
e.multiWayMerge = &multiWayMerge{e.lessRow, make([]partitionPointer, 0, len(e.partitionList))}
for i := 0; i < len(e.partitionList); i++ {
row, err := e.partitionList[i].GetSortedRow(0)
if err != nil {
return err
}
e.multiWayMerge.elements = append(e.multiWayMerge.elements, partitionPointer{row: row, partitionID: i, consumed: 0})
}
heap.Init(e.multiWayMerge)
}
for !req.IsFull() && e.multiWayMerge.Len() > 0 {
partitionPtr := e.multiWayMerge.elements[0]
req.AppendRow(partitionPtr.row)
partitionPtr.consumed++
if partitionPtr.consumed >= e.partitionList[partitionPtr.partitionID].NumRow() {
heap.Remove(e.multiWayMerge, 0)
continue
}
partitionPtr.row, err = e.partitionList[partitionPtr.partitionID].
GetSortedRow(partitionPtr.consumed)
if err != nil {
return err
}
e.multiWayMerge.elements[0] = partitionPtr
heap.Fix(e.multiWayMerge, 0)
}
return nil
}
func (e *SortExec) fetchRowChunks(ctx context.Context) error {
fields := retTypes(e)
byItemsDesc := make([]bool, len(e.ByItems))
for i, byItem := range e.ByItems {
byItemsDesc[i] = byItem.Desc
}
e.rowChunks = chunk.NewSortedRowContainer(fields, e.maxChunkSize, byItemsDesc, e.keyColumns, e.keyCmpFuncs)
e.rowChunks.GetMemTracker().AttachTo(e.memTracker)
e.rowChunks.GetMemTracker().SetLabel(memory.LabelForRowChunks)
if variable.EnableTmpStorageOnOOM.Load() {
e.spillAction = e.rowChunks.ActionSpill()
failpoint.Inject("testSortedRowContainerSpill", func(val failpoint.Value) {
if val.(bool) {
e.spillAction = e.rowChunks.ActionSpillForTest()
defer e.spillAction.WaitForTest()
}
})
e.ctx.GetSessionVars().StmtCtx.MemTracker.FallbackOldAndSetNewAction(e.spillAction)
e.rowChunks.GetDiskTracker().AttachTo(e.diskTracker)
e.rowChunks.GetDiskTracker().SetLabel(memory.LabelForRowChunks)
}
for {
chk := newFirstChunk(e.children[0])
err := Next(ctx, e.children[0], chk)
if err != nil {
return err
}
rowCount := chk.NumRows()
if rowCount == 0 {
break
}
if err := e.rowChunks.Add(chk); err != nil {
if errors.Is(err, chunk.ErrCannotAddBecauseSorted) {
e.partitionList = append(e.partitionList, e.rowChunks)
e.rowChunks = chunk.NewSortedRowContainer(fields, e.maxChunkSize, byItemsDesc, e.keyColumns, e.keyCmpFuncs)
e.rowChunks.GetMemTracker().AttachTo(e.memTracker)
e.rowChunks.GetMemTracker().SetLabel(memory.LabelForRowChunks)
e.rowChunks.GetDiskTracker().AttachTo(e.diskTracker)
e.rowChunks.GetDiskTracker().SetLabel(memory.LabelForRowChunks)
e.spillAction = e.rowChunks.ActionSpill()
failpoint.Inject("testSortedRowContainerSpill", func(val failpoint.Value) {
if val.(bool) {
e.spillAction = e.rowChunks.ActionSpillForTest()
defer e.spillAction.WaitForTest()
}
})
e.ctx.GetSessionVars().StmtCtx.MemTracker.FallbackOldAndSetNewAction(e.spillAction)
err = e.rowChunks.Add(chk)
}
if err != nil {
return err
}
}
}
if e.rowChunks.NumRow() > 0 {
e.rowChunks.Sort()
e.partitionList = append(e.partitionList, e.rowChunks)
}
return nil
}
func (e *SortExec) initCompareFuncs() {
e.keyCmpFuncs = make([]chunk.CompareFunc, len(e.ByItems))
for i := range e.ByItems {
keyType := e.ByItems[i].Expr.GetType()
e.keyCmpFuncs[i] = chunk.GetCompareFunc(keyType)
}
}
func (e *SortExec) buildKeyColumns() {
e.keyColumns = make([]int, 0, len(e.ByItems))
for _, by := range e.ByItems {
col := by.Expr.(*expression.Column)
e.keyColumns = append(e.keyColumns, col.Index)
}
}
func (e *SortExec) lessRow(rowI, rowJ chunk.Row) bool {
for i, colIdx := range e.keyColumns {
cmpFunc := e.keyCmpFuncs[i]
cmp := cmpFunc(rowI, colIdx, rowJ, colIdx)
if e.ByItems[i].Desc {
cmp = -cmp
}
if cmp < 0 {
return true
} else if cmp > 0 {
return false
}
}
return false
}
type partitionPointer struct {
row chunk.Row
partitionID int
consumed int
}
type multiWayMerge struct {
lessRowFunction func(rowI chunk.Row, rowJ chunk.Row) bool
elements []partitionPointer
}
func (h *multiWayMerge) Less(i, j int) bool {
rowI := h.elements[i].row
rowJ := h.elements[j].row
return h.lessRowFunction(rowI, rowJ)
}
func (h *multiWayMerge) Len() int {
return len(h.elements)
}
func (h *multiWayMerge) Push(x interface{}) {
// Should never be called.
}
func (h *multiWayMerge) Pop() interface{} {
h.elements = h.elements[:len(h.elements)-1]
return nil
}
func (h *multiWayMerge) Swap(i, j int) {
h.elements[i], h.elements[j] = h.elements[j], h.elements[i]
}
// TopNExec implements a Top-N algorithm and it is built from a SELECT statement with ORDER BY and LIMIT.
// Instead of sorting all the rows fetched from the table, it keeps the Top-N elements only in a heap to reduce memory usage.
type TopNExec struct {
SortExec
limit *plannercore.PhysicalLimit
totalLimit uint64
// rowChunks is the chunks to store row values.
rowChunks *chunk.List
// rowPointer store the chunk index and row index for each row.
rowPtrs []chunk.RowPtr
chkHeap *topNChunkHeap
}
// topNChunkHeap implements heap.Interface.
type topNChunkHeap struct {
*TopNExec
}
// Less implement heap.Interface, but since we mantains a max heap,
// this function returns true if row i is greater than row j.
func (h *topNChunkHeap) Less(i, j int) bool {
rowI := h.rowChunks.GetRow(h.rowPtrs[i])
rowJ := h.rowChunks.GetRow(h.rowPtrs[j])
return h.greaterRow(rowI, rowJ)
}
func (h *topNChunkHeap) greaterRow(rowI, rowJ chunk.Row) bool {
for i, colIdx := range h.keyColumns {
cmpFunc := h.keyCmpFuncs[i]
cmp := cmpFunc(rowI, colIdx, rowJ, colIdx)
if h.ByItems[i].Desc {
cmp = -cmp
}
if cmp > 0 {
return true
} else if cmp < 0 {
return false
}
}
return false
}
func (h *topNChunkHeap) Len() int {
return len(h.rowPtrs)
}
func (h *topNChunkHeap) Push(x interface{}) {
// Should never be called.
}
func (h *topNChunkHeap) Pop() interface{} {
h.rowPtrs = h.rowPtrs[:len(h.rowPtrs)-1]
// We don't need the popped value, return nil to avoid memory allocation.
return nil
}
func (h *topNChunkHeap) Swap(i, j int) {
h.rowPtrs[i], h.rowPtrs[j] = h.rowPtrs[j], h.rowPtrs[i]
}
// keyColumnsLess is the less function for key columns.
func (e *TopNExec) keyColumnsLess(i, j chunk.RowPtr) bool {
rowI := e.rowChunks.GetRow(i)
rowJ := e.rowChunks.GetRow(j)
return e.lessRow(rowI, rowJ)
}
func (e *TopNExec) initPointers() {
e.rowPtrs = make([]chunk.RowPtr, 0, e.rowChunks.Len())
e.memTracker.Consume(int64(8 * e.rowChunks.Len()))
for chkIdx := 0; chkIdx < e.rowChunks.NumChunks(); chkIdx++ {
rowChk := e.rowChunks.GetChunk(chkIdx)
for rowIdx := 0; rowIdx < rowChk.NumRows(); rowIdx++ {
e.rowPtrs = append(e.rowPtrs, chunk.RowPtr{ChkIdx: uint32(chkIdx), RowIdx: uint32(rowIdx)})
}
}
}
// Open implements the Executor Open interface.
func (e *TopNExec) Open(ctx context.Context) error {
e.memTracker = memory.NewTracker(e.id, -1)
e.memTracker.AttachTo(e.ctx.GetSessionVars().StmtCtx.MemTracker)
e.fetched = false
e.Idx = 0
return e.children[0].Open(ctx)
}
// Next implements the Executor Next interface.
func (e *TopNExec) Next(ctx context.Context, req *chunk.Chunk) error {
req.Reset()
if !e.fetched {
e.totalLimit = e.limit.Offset + e.limit.Count
e.Idx = int(e.limit.Offset)
err := e.loadChunksUntilTotalLimit(ctx)
if err != nil {
return err
}
err = e.executeTopN(ctx)
if err != nil {
return err
}
e.fetched = true
}
if e.Idx >= len(e.rowPtrs) {
return nil
}
if !req.IsFull() {
numToAppend := mathutil.Min(len(e.rowPtrs)-e.Idx, req.RequiredRows()-req.NumRows())
rows := make([]chunk.Row, numToAppend)
for index := 0; index < numToAppend; index++ {
rows[index] = e.rowChunks.GetRow(e.rowPtrs[e.Idx])
e.Idx++
}
req.AppendRows(rows)
}
return nil
}
func (e *TopNExec) loadChunksUntilTotalLimit(ctx context.Context) error {
e.chkHeap = &topNChunkHeap{e}
e.rowChunks = chunk.NewList(retTypes(e), e.initCap, e.maxChunkSize)
e.rowChunks.GetMemTracker().AttachTo(e.memTracker)
e.rowChunks.GetMemTracker().SetLabel(memory.LabelForRowChunks)
for uint64(e.rowChunks.Len()) < e.totalLimit {
srcChk := newFirstChunk(e.children[0])
// adjust required rows by total limit
srcChk.SetRequiredRows(int(e.totalLimit-uint64(e.rowChunks.Len())), e.maxChunkSize)
err := Next(ctx, e.children[0], srcChk)
if err != nil {
return err
}
if srcChk.NumRows() == 0 {
break
}
e.rowChunks.Add(srcChk)
}
e.initPointers()
e.initCompareFuncs()
e.buildKeyColumns()
return nil
}
const topNCompactionFactor = 4
func (e *TopNExec) executeTopN(ctx context.Context) error {
heap.Init(e.chkHeap)
for uint64(len(e.rowPtrs)) > e.totalLimit {
// The number of rows we loaded may exceeds total limit, remove greatest rows by Pop.
heap.Pop(e.chkHeap)
}
childRowChk := newFirstChunk(e.children[0])
for {
err := Next(ctx, e.children[0], childRowChk)
if err != nil {
return err
}
if childRowChk.NumRows() == 0 {
break
}
err = e.processChildChk(childRowChk)
if err != nil {
return err
}
if e.rowChunks.Len() > len(e.rowPtrs)*topNCompactionFactor {
err = e.doCompaction()
if err != nil {
return err
}
}
}
slices.SortFunc(e.rowPtrs, e.keyColumnsLess)
return nil
}
func (e *TopNExec) processChildChk(childRowChk *chunk.Chunk) error {
for i := 0; i < childRowChk.NumRows(); i++ {
heapMaxPtr := e.rowPtrs[0]
var heapMax, next chunk.Row
heapMax = e.rowChunks.GetRow(heapMaxPtr)
next = childRowChk.GetRow(i)
if e.chkHeap.greaterRow(heapMax, next) {
// Evict heap max, keep the next row.
e.rowPtrs[0] = e.rowChunks.AppendRow(childRowChk.GetRow(i))
heap.Fix(e.chkHeap, 0)
}
}
return nil
}
// doCompaction rebuild the chunks and row pointers to release memory.
// If we don't do compaction, in a extreme case like the child data is already ascending sorted
// but we want descending top N, then we will keep all data in memory.
// But if data is distributed randomly, this function will be called log(n) times.
func (e *TopNExec) doCompaction() error {
newRowChunks := chunk.NewList(retTypes(e), e.initCap, e.maxChunkSize)
newRowPtrs := make([]chunk.RowPtr, 0, e.rowChunks.Len())
for _, rowPtr := range e.rowPtrs {
newRowPtr := newRowChunks.AppendRow(e.rowChunks.GetRow(rowPtr))
newRowPtrs = append(newRowPtrs, newRowPtr)
}
newRowChunks.GetMemTracker().SetLabel(memory.LabelForRowChunks)
e.memTracker.ReplaceChild(e.rowChunks.GetMemTracker(), newRowChunks.GetMemTracker())
e.rowChunks = newRowChunks
e.memTracker.Consume(int64(-8 * len(e.rowPtrs)))
e.memTracker.Consume(int64(8 * len(newRowPtrs)))
e.rowPtrs = newRowPtrs
return nil
}
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