app/vmselect/netstorage: reduce tail latency during query processing

Previously the selected time series were split evenly among available CPU cores
for further processing - e.g unpacking the data and applying the given rollup
function to the unpacked data.
Some time series could be processed slower than others.
This could result in uneven work distribution among available CPU cores,
e.g. some CPU cores could complete their work sooner than others.
This could slow down query execution.

The new algorithm allows stealing time series to process from other CPU cores
when all the local work is done. This should reduce the maximum time
needed for query execution (aka tail latency).

The new algorithm should also scale better on systems with many CPU cores,
since every CPU processes locally assigned time series without inter-CPU communications.

The inter-CPU communications are used only when all the local work is finished
and the pending work from other CPUs needs to be stealed.
This commit is contained in:
Aliaksandr Valialkin 2023-01-10 13:06:02 -08:00
parent 158a280822
commit 98931449c1
No known key found for this signature in database
GPG Key ID: A72BEC6CD3D0DED1

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@ -6,10 +6,10 @@ import (
"flag"
"fmt"
"io"
"math/rand"
"net"
"net/http"
"os"
"runtime"
"sort"
"strings"
"sync"
@ -31,7 +31,6 @@ import (
"github.com/VictoriaMetrics/metrics"
"github.com/VictoriaMetrics/metricsql"
"github.com/cespare/xxhash/v2"
"github.com/valyala/fastrand"
)
var (
@ -150,16 +149,66 @@ func (tsw *timeseriesWork) do(r *Result, workerID uint) error {
return nil
}
func timeseriesWorker(tsws []*timeseriesWork, workerID uint) {
func timeseriesWorker(qt *querytracer.Tracer, workChs []chan *timeseriesWork, workerID uint) {
tmpResult := getTmpResult()
// Perform own work at first.
rowsProcessed := 0
seriesProcessed := 0
ch := workChs[workerID]
for tsw := range ch {
tsw.err = tsw.do(&tmpResult.rs, workerID)
rowsProcessed += tsw.rowsProcessed
seriesProcessed++
}
qt.Printf("own work processed: series=%d, samples=%d", seriesProcessed, rowsProcessed)
// Then help others with the remaining work.
rowsProcessed = 0
seriesProcessed = 0
idx := int(workerID)
for {
tsw, idxNext := stealTimeseriesWork(workChs, idx)
if tsw == nil {
// There is no more work
break
}
tsw.err = tsw.do(&tmpResult.rs, workerID)
rowsProcessed += tsw.rowsProcessed
seriesProcessed++
idx = idxNext
}
qt.Printf("others work processed: series=%d, samples=%d", seriesProcessed, rowsProcessed)
putTmpResult(tmpResult)
}
func stealTimeseriesWork(workChs []chan *timeseriesWork, startIdx int) (*timeseriesWork, int) {
for i := startIdx; i < startIdx+len(workChs); i++ {
// Give a chance other goroutines to perform their work
runtime.Gosched()
idx := i % len(workChs)
ch := workChs[idx]
// It is expected that every channel in the workChs is already closed,
// so the next line should return immediately.
tsw, ok := <-ch
if ok {
return tsw, idx
}
}
return nil, startIdx
}
func getTmpResult() *result {
v := resultPool.Get()
if v == nil {
v = &result{}
}
r := v.(*result)
for _, tsw := range tsws {
err := tsw.do(&r.rs, workerID)
tsw.err = err
}
return v.(*result)
}
func putTmpResult(r *result) {
currentTime := fasttime.UnixTimestamp()
if cap(r.rs.Values) > 1024*1024 && 4*len(r.rs.Values) < cap(r.rs.Values) && currentTime-r.lastResetTime > 10 {
// Reset r.rs in order to preseve memory usage after processing big time series with millions of rows.
@ -187,87 +236,113 @@ func (rss *Results) RunParallel(qt *querytracer.Tracer, f func(rs *Result, worke
qt = qt.NewChild("parallel process of fetched data")
defer rss.closeTmpBlockFiles()
// Prepare work for workers.
tsws := make([]*timeseriesWork, len(rss.packedTimeseries))
rowsProcessedTotal, err := rss.runParallel(qt, f)
seriesProcessedTotal := len(rss.packedTimeseries)
rss.packedTimeseries = rss.packedTimeseries[:0]
rowsReadPerQuery.Update(float64(rowsProcessedTotal))
seriesReadPerQuery.Update(float64(seriesProcessedTotal))
qt.Donef("series=%d, samples=%d", seriesProcessedTotal, rowsProcessedTotal)
return err
}
func (rss *Results) runParallel(qt *querytracer.Tracer, f func(rs *Result, workerID uint) error) (int, error) {
tswsLen := len(rss.packedTimeseries)
if tswsLen == 0 {
// Nothing to process
return 0, nil
}
var mustStop uint32
for i := range rss.packedTimeseries {
tsw := getTimeseriesWork()
initTimeseriesWork := func(tsw *timeseriesWork, pts *packedTimeseries) {
tsw.rss = rss
tsw.pts = &rss.packedTimeseries[i]
tsw.pts = pts
tsw.f = f
tsw.mustStop = &mustStop
}
if gomaxprocs == 1 || tswsLen == 1 {
// It is faster to process time series in the current goroutine.
tsw := getTimeseriesWork()
tmpResult := getTmpResult()
rowsProcessedTotal := 0
var err error
for i := range rss.packedTimeseries {
initTimeseriesWork(tsw, &rss.packedTimeseries[i])
err = tsw.do(&tmpResult.rs, 0)
rowsReadPerSeries.Update(float64(tsw.rowsProcessed))
rowsProcessedTotal += tsw.rowsProcessed
if err != nil {
break
}
tsw.reset()
}
putTmpResult(tmpResult)
putTimeseriesWork(tsw)
return rowsProcessedTotal, err
}
// Slow path - spin up multiple local workers for parallel data processing.
// Do not use global workers pool, since it increases inter-CPU memory ping-poing,
// which reduces the scalability on systems with many CPU cores.
// Prepare the work for workers.
tsws := make([]*timeseriesWork, len(rss.packedTimeseries))
for i := range rss.packedTimeseries {
tsw := getTimeseriesWork()
initTimeseriesWork(tsw, &rss.packedTimeseries[i])
tsws[i] = tsw
}
// Shuffle tsws for providing the equal amount of work among workers.
r := getRand()
r.Shuffle(len(tsws), func(i, j int) {
tsws[i], tsws[j] = tsws[j], tsws[i]
})
putRand(r)
// Spin up up to gomaxprocs local workers and split work equally among them.
// This guarantees linear scalability with the increase of gomaxprocs
// (e.g. the number of available CPU cores).
itemsPerWorker := 1
if len(rss.packedTimeseries) > gomaxprocs {
itemsPerWorker = (len(rss.packedTimeseries) + gomaxprocs - 1) / gomaxprocs
// Prepare worker channels.
workers := len(tsws)
if workers > gomaxprocs {
workers = gomaxprocs
}
var start int
var i uint
itemsPerWorker := (len(tsws) + workers - 1) / workers
workChs := make([]chan *timeseriesWork, workers)
for i := range workChs {
workChs[i] = make(chan *timeseriesWork, itemsPerWorker)
}
// Spread work among workers.
for i, tsw := range tsws {
idx := i % len(workChs)
workChs[idx] <- tsw
}
// Mark worker channels as closed.
for _, workCh := range workChs {
close(workCh)
}
// Start workers and wait until they finish the work.
var wg sync.WaitGroup
for start < len(tsws) {
end := start + itemsPerWorker
if end > len(tsws) {
end = len(tsws)
}
chunk := tsws[start:end]
for i := range workChs {
wg.Add(1)
go func(tswsChunk []*timeseriesWork, workerID uint) {
defer wg.Done()
timeseriesWorker(tswsChunk, workerID)
}(chunk, i)
start = end
i++
qtChild := qt.NewChild("worker #%d", i)
go func(workerID uint) {
timeseriesWorker(qtChild, workChs, workerID)
qtChild.Done()
wg.Done()
}(uint(i))
}
// Wait until work is complete.
wg.Wait()
// Collect results.
var firstErr error
rowsProcessedTotal := 0
for _, tsw := range tsws {
if err := tsw.err; err != nil && firstErr == nil {
if tsw.err != nil && firstErr == nil {
// Return just the first error, since other errors are likely duplicate the first error.
firstErr = err
firstErr = tsw.err
}
rowsReadPerSeries.Update(float64(tsw.rowsProcessed))
rowsProcessedTotal += tsw.rowsProcessed
putTimeseriesWork(tsw)
}
seriesProcessedTotal := len(rss.packedTimeseries)
rss.packedTimeseries = rss.packedTimeseries[:0]
rowsReadPerQuery.Update(float64(rowsProcessedTotal))
seriesReadPerQuery.Update(float64(seriesProcessedTotal))
qt.Donef("series=%d, samples=%d", seriesProcessedTotal, rowsProcessedTotal)
return firstErr
}
var randPool sync.Pool
func getRand() *rand.Rand {
v := randPool.Get()
if v == nil {
v = rand.New(rand.NewSource(int64(fasttime.UnixTimestamp())))
}
return v.(*rand.Rand)
}
func putRand(r *rand.Rand) {
randPool.Put(r)
return rowsProcessedTotal, firstErr
}
var (
@ -283,48 +358,30 @@ type packedTimeseries struct {
addrs []tmpBlockAddr
}
type unpackWorkItem struct {
type unpackWork struct {
tbfs []*tmpBlocksFile
addr tmpBlockAddr
tr storage.TimeRange
}
type unpackWork struct {
ws []unpackWorkItem
tbfs []*tmpBlocksFile
sbs []*sortBlock
doneCh chan error
sb *sortBlock
err error
}
func (upw *unpackWork) reset() {
ws := upw.ws
for i := range ws {
w := &ws[i]
w.addr = tmpBlockAddr{}
w.tr = storage.TimeRange{}
}
upw.ws = upw.ws[:0]
upw.tbfs = nil
sbs := upw.sbs
for i := range sbs {
sbs[i] = nil
}
upw.sbs = upw.sbs[:0]
if n := len(upw.doneCh); n > 0 {
logger.Panicf("BUG: upw.doneCh must be empty; it contains %d items now", n)
}
upw.addr = tmpBlockAddr{}
upw.tr = storage.TimeRange{}
upw.sb = nil
upw.err = nil
}
func (upw *unpackWork) unpack(tmpBlock *storage.Block) {
for _, w := range upw.ws {
sb := getSortBlock()
if err := sb.unpackFrom(tmpBlock, upw.tbfs, w.addr, w.tr); err != nil {
putSortBlock(sb)
upw.doneCh <- fmt.Errorf("cannot unpack block: %w", err)
return
}
upw.sbs = append(upw.sbs, sb)
sb := getSortBlock()
if err := sb.unpackFrom(tmpBlock, upw.tbfs, upw.addr, upw.tr); err != nil {
putSortBlock(sb)
upw.err = fmt.Errorf("cannot unpack block: %w", err)
return
}
upw.doneCh <- nil
upw.sb = sb
}
func getUnpackWork() *unpackWork {
@ -332,9 +389,7 @@ func getUnpackWork() *unpackWork {
if v != nil {
return v.(*unpackWork)
}
return &unpackWork{
doneCh: make(chan error, 1),
}
return &unpackWork{}
}
func putUnpackWork(upw *unpackWork) {
@ -344,36 +399,47 @@ func putUnpackWork(upw *unpackWork) {
var unpackWorkPool sync.Pool
func scheduleUnpackWork(workChs []chan *unpackWork, uw *unpackWork) {
if len(workChs) == 1 {
// Fast path for a single worker
workChs[0] <- uw
return
}
attempts := 0
for {
idx := fastrand.Uint32n(uint32(len(workChs)))
select {
case workChs[idx] <- uw:
return
default:
attempts++
if attempts >= len(workChs) {
workChs[idx] <- uw
return
}
}
}
}
func unpackWorker(ch <-chan *unpackWork) {
func unpackWorker(workChs []chan *unpackWork, workerID uint) {
tmpBlock := getTmpStorageBlock()
// Deal with own work at first.
ch := workChs[workerID]
for upw := range ch {
upw.unpack(tmpBlock)
}
// Then help others with their work.
idx := int(workerID)
for {
upw, idxNext := stealUnpackWork(workChs, idx)
if upw == nil {
// There is no more work
break
}
upw.unpack(tmpBlock)
idx = idxNext
}
putTmpStorageBlock(tmpBlock)
}
func stealUnpackWork(workChs []chan *unpackWork, startIdx int) (*unpackWork, int) {
for i := startIdx; i < startIdx+len(workChs); i++ {
// Give a chance other goroutines to perform their work
runtime.Gosched()
idx := i % len(workChs)
ch := workChs[idx]
// It is expected that every channel in the workChs is already closed,
// so the next line should return immediately.
upw, ok := <-ch
if ok {
return upw, idx
}
}
return nil, startIdx
}
func getTmpStorageBlock() *storage.Block {
v := tmpStorageBlockPool.Get()
if v == nil {
@ -388,14 +454,6 @@ func putTmpStorageBlock(sb *storage.Block) {
var tmpStorageBlockPool sync.Pool
// unpackBatchSize is the maximum number of blocks that may be unpacked at once by a single goroutine.
//
// It is better to load a single goroutine for up to 100ms on a system with many CPU cores
// in order to reduce inter-CPU memory ping-pong.
// A single goroutine can unpack up to 40 millions of rows per second, while a single block contains up to 8K rows.
// So the batch size should be 100ms * 40M / 8K = 500.
var unpackBatchSize = 500
// Unpack unpacks pts to dst.
func (pts *packedTimeseries) Unpack(dst *Result, tbfs []*tmpBlocksFile, tr storage.TimeRange) error {
dst.reset()
@ -405,6 +463,7 @@ func (pts *packedTimeseries) Unpack(dst *Result, tbfs []*tmpBlocksFile, tr stora
sbh := getSortBlocksHeap()
var err error
sbh.sbs, err = pts.unpackTo(sbh.sbs[:0], tbfs, tr)
pts.addrs = pts.addrs[:0]
if err != nil {
putSortBlocksHeap(sbh)
return err
@ -416,112 +475,114 @@ func (pts *packedTimeseries) Unpack(dst *Result, tbfs []*tmpBlocksFile, tr stora
}
func (pts *packedTimeseries) unpackTo(dst []*sortBlock, tbfs []*tmpBlocksFile, tr storage.TimeRange) ([]*sortBlock, error) {
addrsLen := len(pts.addrs)
upwsLen := (addrsLen + unpackBatchSize - 1) / unpackBatchSize
if upwsLen == 1 {
// Fast path for common case - unpack all the data in the current goroutine
upw := getUnpackWork()
upwsLen := len(pts.addrs)
if upwsLen == 0 {
// Nothing to do
return nil, nil
}
initUnpackWork := func(upw *unpackWork, addr tmpBlockAddr) {
upw.tbfs = tbfs
for _, addr := range pts.addrs {
upw.ws = append(upw.ws, unpackWorkItem{
addr: addr,
tr: tr,
})
}
pts.addrs = pts.addrs[:0]
tmpBlock := getTmpStorageBlock()
upw.unpack(tmpBlock)
putTmpStorageBlock(tmpBlock)
if err := <-upw.doneCh; err != nil {
return dst, err
}
upw.addr = addr
upw.tr = tr
}
if gomaxprocs == 1 || upwsLen == 1 {
// It is faster to unpack all the data in the current goroutine.
upw := getUnpackWork()
samples := 0
for _, sb := range upw.sbs {
samples += len(sb.Timestamps)
if *maxSamplesPerSeries > 0 && samples > *maxSamplesPerSeries {
return dst, fmt.Errorf("cannot process more than %d samples per series; either increase -search.maxSamplesPerSeries "+
"or reduce time range for the query", *maxSamplesPerSeries)
tmpBlock := getTmpStorageBlock()
var err error
for _, addr := range pts.addrs {
initUnpackWork(upw, addr)
upw.unpack(tmpBlock)
if upw.err != nil {
return dst, upw.err
}
dst = append(dst, sb)
samples += len(upw.sb.Timestamps)
if *maxSamplesPerSeries > 0 && samples > *maxSamplesPerSeries {
putSortBlock(upw.sb)
err = fmt.Errorf("cannot process more than %d samples per series; either increase -search.maxSamplesPerSeries "+
"or reduce time range for the query", *maxSamplesPerSeries)
break
}
dst = append(dst, upw.sb)
upw.reset()
}
putTmpStorageBlock(tmpBlock)
putUnpackWork(upw)
return dst, nil
return dst, err
}
// Slow path - spin up multiple local workers for parallel data unpacking.
// Do not use global workers pool, since it increases inter-CPU memory ping-poing,
// which reduces the scalability on systems with many CPU cores.
workers := upwsLen
// Prepare the work for workers.
upws := make([]*unpackWork, upwsLen)
for i, addr := range pts.addrs {
upw := getUnpackWork()
initUnpackWork(upw, addr)
upws[i] = upw
}
// Prepare worker channels.
workers := len(upws)
if workers > gomaxprocs {
workers = gomaxprocs
}
if workers < 1 {
workers = 1
}
itemsPerWorker := (len(upws) + workers - 1) / workers
workChs := make([]chan *unpackWork, workers)
var workChsWG sync.WaitGroup
for i := 0; i < workers; i++ {
workChs[i] = make(chan *unpackWork, 1)
workChsWG.Add(1)
go func(workerID int) {
defer workChsWG.Done()
unpackWorker(workChs[workerID])
}(i)
for i := range workChs {
workChs[i] = make(chan *unpackWork, itemsPerWorker)
}
// Feed workers with work
upws := make([]*unpackWork, 0, upwsLen)
upw := getUnpackWork()
upw.tbfs = tbfs
for _, addr := range pts.addrs {
if len(upw.ws) >= unpackBatchSize {
scheduleUnpackWork(workChs, upw)
upws = append(upws, upw)
upw = getUnpackWork()
upw.tbfs = tbfs
}
upw.ws = append(upw.ws, unpackWorkItem{
addr: addr,
tr: tr,
})
// Spread work among worker channels.
for i, upw := range upws {
idx := i % len(workChs)
workChs[idx] <- upw
}
scheduleUnpackWork(workChs, upw)
upws = append(upws, upw)
pts.addrs = pts.addrs[:0]
// Collect the unpacked sortBlock items
samples := 0
var firstErr error
for _, upw := range upws {
if err := <-upw.doneCh; err != nil && firstErr == nil {
// Return the first error only, since other errors are likely the same.
firstErr = err
}
if firstErr == nil {
for _, sb := range upw.sbs {
samples += len(sb.Timestamps)
if *maxSamplesPerSeries > 0 && samples > *maxSamplesPerSeries {
firstErr = fmt.Errorf("cannot process more than %d samples per series; either increase -search.maxSamplesPerSeries "+
"or reduce time range for the query", *maxSamplesPerSeries)
break
}
dst = append(dst, sb)
}
} else {
for _, sb := range upw.sbs {
putSortBlock(sb)
}
}
putUnpackWork(upw)
}
// Shut down local workers
// Mark worker channels as closed.
for _, workCh := range workChs {
close(workCh)
}
workChsWG.Wait()
// Start workers and wait until they finish the work.
var wg sync.WaitGroup
for i := 0; i < workers; i++ {
wg.Add(1)
go func(workerID uint) {
unpackWorker(workChs, workerID)
wg.Done()
}(uint(i))
}
wg.Wait()
// Collect results.
samples := 0
var firstErr error
for _, upw := range upws {
if upw.err != nil && firstErr == nil {
// Return the first error only, since other errors are likely the same.
firstErr = upw.err
}
if firstErr == nil {
sb := upw.sb
samples += len(sb.Timestamps)
if *maxSamplesPerSeries > 0 && samples > *maxSamplesPerSeries {
putSortBlock(sb)
firstErr = fmt.Errorf("cannot process more than %d samples per series; either increase -search.maxSamplesPerSeries "+
"or reduce time range for the query", *maxSamplesPerSeries)
} else {
dst = append(dst, sb)
}
} else {
putSortBlock(upw.sb)
}
putUnpackWork(upw)
}
return dst, firstErr
}