app/vmselect: improve performance scalability on multi-CPU systems for /api/v1/export/... endpoints

app/vmselect/clusternative/vmselect.go

@@ -112,7 +112,7 @@ func newBlockIterator(qt *querytracer.Tracer, denyPartialResponse bool, sq *stor
 	bi.workCh = make(chan workItem, 16)
 	bi.wg.Add(1)
 	go func() {
-		_, err := netstorage.ProcessBlocks(qt, denyPartialResponse, sq, func(mb *storage.MetricBlock, workerIdx int) error {
+		_, err := netstorage.ProcessBlocks(qt, denyPartialResponse, sq, func(mb *storage.MetricBlock, workerID uint) error {
 			wi := workItem{
 				mb:     mb,
 				doneCh: make(chan struct{}),

app/vmselect/netstorage/netstorage.go

@@ -662,9 +662,9 @@ func RegisterMetricNames(qt *querytracer.Tracer, mrs []storage.MetricRow, deadli
 	}
 
 	// Push mrs to storage nodes in parallel.
-	snr := startStorageNodesRequest(qt, true, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, true, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.registerMetricNamesRequests.Inc()
-		err := sn.registerMetricNames(qt, mrsPerNode[workerIdx], deadline)
+		err := sn.registerMetricNames(qt, mrsPerNode[workerID], deadline)
 		if err != nil {
 			sn.registerMetricNamesErrors.Inc()
 		}
@@ -693,7 +693,7 @@ func DeleteSeries(qt *querytracer.Tracer, sq *storage.SearchQuery, deadline sear
 		deletedCount int
 		err          error
 	}
-	snr := startStorageNodesRequest(qt, true, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, true, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.deleteSeriesRequests.Inc()
 		deletedCount, err := sn.deleteSeries(qt, requestData, deadline)
 		if err != nil {
@@ -734,7 +734,7 @@ func LabelNames(qt *querytracer.Tracer, denyPartialResponse bool, sq *storage.Se
 		labelNames []string
 		err        error
 	}
-	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.labelNamesRequests.Inc()
 		labelNames, err := sn.getLabelNames(qt, requestData, maxLabelNames, deadline)
 		if err != nil {
@@ -836,7 +836,7 @@ func LabelValues(qt *querytracer.Tracer, denyPartialResponse bool, labelName str
 		labelValues []string
 		err         error
 	}
-	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.labelValuesRequests.Inc()
 		labelValues, err := sn.getLabelValues(qt, labelName, requestData, maxLabelValues, deadline)
 		if err != nil {
@@ -918,7 +918,7 @@ func TagValueSuffixes(qt *querytracer.Tracer, accountID, projectID uint32, denyP
 		suffixes []string
 		err      error
 	}
-	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.tagValueSuffixesRequests.Inc()
 		suffixes, err := sn.getTagValueSuffixes(qt, accountID, projectID, tr, tagKey, tagValuePrefix, delimiter, maxSuffixes, deadline)
 		if err != nil {
@@ -982,7 +982,7 @@ func TSDBStatus(qt *querytracer.Tracer, denyPartialResponse bool, sq *storage.Se
 		status *storage.TSDBStatus
 		err    error
 	}
-	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.tsdbStatusRequests.Inc()
 		status, err := sn.getTSDBStatus(qt, requestData, focusLabel, topN, deadline)
 		if err != nil {
@@ -1087,7 +1087,7 @@ func SeriesCount(qt *querytracer.Tracer, accountID, projectID uint32, denyPartia
 		n   uint64
 		err error
 	}
-	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.seriesCountRequests.Inc()
 		n, err := sn.getSeriesCount(qt, accountID, projectID, deadline)
 		if err != nil {
@@ -1139,16 +1139,16 @@ func newTmpBlocksFileWrapper() *tmpBlocksFileWrapper {
 	}
 }
 
-func (tbfw *tmpBlocksFileWrapper) RegisterAndWriteBlock(mb *storage.MetricBlock, workerIdx int) error {
+func (tbfw *tmpBlocksFileWrapper) RegisterAndWriteBlock(mb *storage.MetricBlock, workerID uint) error {
 	bb := tmpBufPool.Get()
 	bb.B = storage.MarshalBlock(bb.B[:0], &mb.Block)
-	addr, err := tbfw.tbfs[workerIdx].WriteBlockData(bb.B, workerIdx)
+	addr, err := tbfw.tbfs[workerID].WriteBlockData(bb.B, workerID)
 	tmpBufPool.Put(bb)
 	if err != nil {
 		return err
 	}
 	metricName := mb.MetricName
-	m := tbfw.ms[workerIdx]
+	m := tbfw.ms[workerID]
 	addrs := m[string(metricName)]
 	addrs = append(addrs, addr)
 	if len(addrs) > 1 {
@@ -1156,11 +1156,11 @@ func (tbfw *tmpBlocksFileWrapper) RegisterAndWriteBlock(mb *storage.MetricBlock,
 	} else {
 		// An optimization for big number of time series with long names: store only a single copy of metricNameStr
 		// in both tbfw.orderedMetricNamess and tbfw.ms.
-		orderedMetricNames := tbfw.orderedMetricNamess[workerIdx]
+		orderedMetricNames := tbfw.orderedMetricNamess[workerID]
 		orderedMetricNames = append(orderedMetricNames, string(metricName))
 		metricNameStr := orderedMetricNames[len(orderedMetricNames)-1]
 		m[metricNameStr] = addrs
-		tbfw.orderedMetricNamess[workerIdx] = orderedMetricNames
+		tbfw.orderedMetricNamess[workerID] = orderedMetricNames
 	}
 	return nil
 }
@@ -1200,7 +1200,7 @@ var metricNamePool = &sync.Pool{
 // It is the responsibility of f to call b.UnmarshalData before reading timestamps and values from the block.
 // It is the responsibility of f to filter blocks according to the given tr.
 func ExportBlocks(qt *querytracer.Tracer, sq *storage.SearchQuery, deadline searchutils.Deadline,
-	f func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange) error) error {
+	f func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange, workerID uint) error) error {
 	qt = qt.NewChild("export blocks: %s", sq)
 	defer qt.Done()
 	if deadline.Exceeded() {
@@ -1212,18 +1212,18 @@ func ExportBlocks(qt *querytracer.Tracer, sq *storage.SearchQuery, deadline sear
 	}
 	blocksRead := newPerNodeCounter()
 	samples := newPerNodeCounter()
-	processBlock := func(mb *storage.MetricBlock, workerIdx int) error {
+	processBlock := func(mb *storage.MetricBlock, workerID uint) error {
 		mn := metricNamePool.Get().(*storage.MetricName)
 		if err := mn.Unmarshal(mb.MetricName); err != nil {
 			return fmt.Errorf("cannot unmarshal metricName: %w", err)
 		}
-		if err := f(mn, &mb.Block, tr); err != nil {
+		if err := f(mn, &mb.Block, tr, workerID); err != nil {
 			return err
 		}
 		mn.Reset()
 		metricNamePool.Put(mn)
-		blocksRead.Add(workerIdx, 1)
+		blocksRead.Add(workerID, 1)
-		samples.Add(workerIdx, uint64(mb.Block.RowsCount()))
+		samples.Add(workerID, uint64(mb.Block.RowsCount()))
 		return nil
 	}
 	_, err := ProcessBlocks(qt, true, sq, processBlock, deadline)
@@ -1250,7 +1250,7 @@ func SearchMetricNames(qt *querytracer.Tracer, denyPartialResponse bool, sq *sto
 		metricNames []string
 		err         error
 	}
-	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.searchMetricNamesRequests.Inc()
 		metricNames, err := sn.processSearchMetricNames(qt, requestData, deadline)
 		if err != nil {
@@ -1307,15 +1307,15 @@ func ProcessSearchQuery(qt *querytracer.Tracer, denyPartialResponse bool, sq *st
 	blocksRead := newPerNodeCounter()
 	samples := newPerNodeCounter()
 	maxSamplesPerWorker := uint64(*maxSamplesPerQuery) / uint64(len(storageNodes))
-	processBlock := func(mb *storage.MetricBlock, workerIdx int) error {
+	processBlock := func(mb *storage.MetricBlock, workerID uint) error {
-		blocksRead.Add(workerIdx, 1)
+		blocksRead.Add(workerID, 1)
-		n := samples.Add(workerIdx, uint64(mb.Block.RowsCount()))
+		n := samples.Add(workerID, uint64(mb.Block.RowsCount()))
 		if *maxSamplesPerQuery > 0 && n > maxSamplesPerWorker && samples.GetTotal() > uint64(*maxSamplesPerQuery) {
 			return fmt.Errorf("cannot select more than -search.maxSamplesPerQuery=%d samples; possible solutions: "+
 				"to increase the -search.maxSamplesPerQuery; to reduce time range for the query; "+
 				"to use more specific label filters in order to select lower number of series", *maxSamplesPerQuery)
 		}
-		if err := tbfw.RegisterAndWriteBlock(mb, workerIdx); err != nil {
+		if err := tbfw.RegisterAndWriteBlock(mb, workerID); err != nil {
 			return fmt.Errorf("cannot write MetricBlock to temporary blocks file: %w", err)
 		}
 		return nil
@@ -1348,7 +1348,7 @@ func ProcessSearchQuery(qt *querytracer.Tracer, denyPartialResponse bool, sq *st
 
 // ProcessBlocks calls processBlock per each block matching the given sq.
 func ProcessBlocks(qt *querytracer.Tracer, denyPartialResponse bool, sq *storage.SearchQuery,
-	processBlock func(mb *storage.MetricBlock, workerIdx int) error, deadline searchutils.Deadline) (bool, error) {
+	processBlock func(mb *storage.MetricBlock, workerID uint) error, deadline searchutils.Deadline) (bool, error) {
 	requestData := sq.Marshal(nil)
 
 	// Make sure that processBlock is no longer called after the exit from ProcessBlocks() function.
@@ -1371,8 +1371,8 @@ func ProcessBlocks(qt *querytracer.Tracer, denyPartialResponse bool, sq *storage
 		_ [128 - unsafe.Sizeof(wgStruct{})%128]byte
 	}
 	wgs := make([]wgWithPadding, len(storageNodes))
-	f := func(mb *storage.MetricBlock, workerIdx int) error {
+	f := func(mb *storage.MetricBlock, workerID uint) error {
-		muwg := &wgs[workerIdx]
+		muwg := &wgs[workerID]
 		muwg.mu.Lock()
 		if muwg.stop {
 			muwg.mu.Unlock()
@@ -1380,15 +1380,15 @@ func ProcessBlocks(qt *querytracer.Tracer, denyPartialResponse bool, sq *storage
 		}
 		muwg.wg.Add(1)
 		muwg.mu.Unlock()
-		err := processBlock(mb, workerIdx)
+		err := processBlock(mb, workerID)
 		muwg.wg.Done()
 		return err
 	}
 
 	// Send the query to all the storage nodes in parallel.
-	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{} {
+	snr := startStorageNodesRequest(qt, denyPartialResponse, func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{} {
 		sn.searchRequests.Inc()
-		err := sn.processSearchQuery(qt, requestData, f, workerIdx, deadline)
+		err := sn.processSearchQuery(qt, requestData, f, workerID, deadline)
 		if err != nil {
 			sn.searchErrors.Inc()
 			err = fmt.Errorf("cannot perform search on vmstorage %s: %w", sn.connPool.Addr(), err)
@@ -1422,15 +1422,15 @@ type storageNodesRequest struct {
 	resultsCh           chan interface{}
 }
 
-func startStorageNodesRequest(qt *querytracer.Tracer, denyPartialResponse bool, f func(qt *querytracer.Tracer, workerIdx int, sn *storageNode) interface{}) *storageNodesRequest {
+func startStorageNodesRequest(qt *querytracer.Tracer, denyPartialResponse bool, f func(qt *querytracer.Tracer, workerID uint, sn *storageNode) interface{}) *storageNodesRequest {
 	resultsCh := make(chan interface{}, len(storageNodes))
 	for idx, sn := range storageNodes {
 		qtChild := qt.NewChild("rpc at vmstorage %s", sn.connPool.Addr())
-		go func(workerIdx int, sn *storageNode) {
+		go func(workerID uint, sn *storageNode) {
-			result := f(qtChild, workerIdx, sn)
+			result := f(qtChild, workerID, sn)
 			resultsCh <- result
 			qtChild.Done()
-		}(idx, sn)
+		}(uint(idx), sn)
 	}
 	return &storageNodesRequest{
 		denyPartialResponse: denyPartialResponse,
@@ -1697,10 +1697,10 @@ func (sn *storageNode) processSearchMetricNames(qt *querytracer.Tracer, requestD
 	return metricNames, nil
 }
 
-func (sn *storageNode) processSearchQuery(qt *querytracer.Tracer, requestData []byte, processBlock func(mb *storage.MetricBlock, workerIdx int) error,
+func (sn *storageNode) processSearchQuery(qt *querytracer.Tracer, requestData []byte, processBlock func(mb *storage.MetricBlock, workerID uint) error,
-	workerIdx int, deadline searchutils.Deadline) error {
+	workerID uint, deadline searchutils.Deadline) error {
 	f := func(bc *handshake.BufferedConn) error {
-		if err := sn.processSearchQueryOnConn(bc, requestData, processBlock, workerIdx); err != nil {
+		if err := sn.processSearchQueryOnConn(bc, requestData, processBlock, workerID); err != nil {
 			return err
 		}
 		return nil
@@ -2201,7 +2201,7 @@ func (sn *storageNode) processSearchMetricNamesOnConn(bc *handshake.BufferedConn
 const maxMetricNameSize = 64 * 1024
 
 func (sn *storageNode) processSearchQueryOnConn(bc *handshake.BufferedConn, requestData []byte,
-	processBlock func(mb *storage.MetricBlock, workerIdx int) error, workerIdx int) error {
+	processBlock func(mb *storage.MetricBlock, workerID uint) error, workerID uint) error {
 	// Send the request to sn.
 	if err := writeBytes(bc, requestData); err != nil {
 		return fmt.Errorf("cannot write requestData: %w", err)
@@ -2241,7 +2241,7 @@ func (sn *storageNode) processSearchQueryOnConn(bc *handshake.BufferedConn, requ
 		blocksRead++
 		sn.metricBlocksRead.Inc()
 		sn.metricRowsRead.Add(mb.Block.RowsCount())
-		if err := processBlock(&mb, workerIdx); err != nil {
+		if err := processBlock(&mb, workerID); err != nil {
 			return fmt.Errorf("cannot process MetricBlock #%d: %w", blocksRead, err)
 		}
 	}
@@ -2440,7 +2440,7 @@ func newPerNodeCounter() *perNodeCounter {
 	}
 }
 
-func (pnc *perNodeCounter) Add(nodeIdx int, n uint64) uint64 {
+func (pnc *perNodeCounter) Add(nodeIdx uint, n uint64) uint64 {
 	return atomic.AddUint64(&pnc.ns[nodeIdx].n, n)
 }
 

app/vmselect/netstorage/tmp_blocks_file.go

@@ -78,7 +78,7 @@ var tmpBlocksFilePool sync.Pool
 type tmpBlockAddr struct {
 	offset uint64
 	size   int
-	tbfIdx int
+	tbfIdx uint
 }
 
 func (addr tmpBlockAddr) String() string {
@@ -96,7 +96,7 @@ var (
 //
 // It returns errors since the operation may fail on space shortage
 // and this must be handled.
-func (tbf *tmpBlocksFile) WriteBlockData(b []byte, tbfIdx int) (tmpBlockAddr, error) {
+func (tbf *tmpBlocksFile) WriteBlockData(b []byte, tbfIdx uint) (tmpBlockAddr, error) {
 	var addr tmpBlockAddr
 	addr.tbfIdx = tbfIdx
 	addr.offset = tbf.offset

app/vmselect/prometheus/export.qtpl

@@ -126,49 +126,24 @@
 }
 {% endfunc %}
 
-{% func ExportPromAPIResponse(resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) %}
+{% func ExportPromAPIHeader() %}
 {
-	{% code
-		lines := 0
-		bytesTotal := 0
-	%}
 	"status":"success",
 	"data":{
 		"resultType":"matrix",
 		"result":[
-			{% code bb, ok := <-resultsCh %}
+{% endfunc %}
-			{% if ok %}
+
-				{%z= bb.B %}
+{% func ExportPromAPIFooter(qt *querytracer.Tracer) %}
-				{% code
-					lines++
-					bytesTotal += len(bb.B)
-					quicktemplate.ReleaseByteBuffer(bb)
-				%}
-				{% for bb := range resultsCh %}
-					,{%z= bb.B %}
-					{% code
-						lines++
-						bytesTotal += len(bb.B)
-						quicktemplate.ReleaseByteBuffer(bb)
-					%}
-				{% endfor %}
-			{% endif %}
 		]
 	}
 	{% code
-		qt.Donef("export format=promapi: lines=%d, bytes=%d", lines, bytesTotal)
+		qt.Donef("export format=promapi")
 	%}
 	{%= dumpQueryTrace(qt) %}
 }
 {% endfunc %}
 
-{% func ExportStdResponse(resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) %}
-	{% for bb := range resultsCh %}
-		{%z= bb.B %}
-		{% code quicktemplate.ReleaseByteBuffer(bb) %}
-	{% endfor %}
-{% endfunc %}
-
 {% func prometheusMetricName(mn *storage.MetricName) %}
 	{%z= mn.MetricGroup %}
 	{% if len(mn.Tags) > 0 %}

app/vmselect/prometheus/export.qtpl.go

@@ -415,184 +415,142 @@ func ExportPromAPILine(xb *exportBlock) string {
 }
 
 //line app/vmselect/prometheus/export.qtpl:129
-func StreamExportPromAPIResponse(qw422016 *qt422016.Writer, resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) {
+func StreamExportPromAPIHeader(qw422016 *qt422016.Writer) {
 //line app/vmselect/prometheus/export.qtpl:129
-	qw422016.N().S(`{`)
+	qw422016.N().S(`{"status":"success","data":{"resultType":"matrix","result":[`)
-//line app/vmselect/prometheus/export.qtpl:132
+//line app/vmselect/prometheus/export.qtpl:135
-	lines := 0
+}
-	bytesTotal := 0
 
-//line app/vmselect/prometheus/export.qtpl:134
+//line app/vmselect/prometheus/export.qtpl:135
-	qw422016.N().S(`"status":"success","data":{"resultType":"matrix","result":[`)
+func WriteExportPromAPIHeader(qq422016 qtio422016.Writer) {
-//line app/vmselect/prometheus/export.qtpl:139
+//line app/vmselect/prometheus/export.qtpl:135
-	bb, ok := <-resultsCh
+	qw422016 := qt422016.AcquireWriter(qq422016)
+//line app/vmselect/prometheus/export.qtpl:135
+	StreamExportPromAPIHeader(qw422016)
+//line app/vmselect/prometheus/export.qtpl:135
+	qt422016.ReleaseWriter(qw422016)
+//line app/vmselect/prometheus/export.qtpl:135
+}
 
-//line app/vmselect/prometheus/export.qtpl:140
+//line app/vmselect/prometheus/export.qtpl:135
-	if ok {
+func ExportPromAPIHeader() string {
-//line app/vmselect/prometheus/export.qtpl:141
+//line app/vmselect/prometheus/export.qtpl:135
-		qw422016.N().Z(bb.B)
+	qb422016 := qt422016.AcquireByteBuffer()
-//line app/vmselect/prometheus/export.qtpl:143
+//line app/vmselect/prometheus/export.qtpl:135
-		lines++
+	WriteExportPromAPIHeader(qb422016)
-		bytesTotal += len(bb.B)
+//line app/vmselect/prometheus/export.qtpl:135
-		quicktemplate.ReleaseByteBuffer(bb)
+	qs422016 := string(qb422016.B)
+//line app/vmselect/prometheus/export.qtpl:135
+	qt422016.ReleaseByteBuffer(qb422016)
+//line app/vmselect/prometheus/export.qtpl:135
+	return qs422016
+//line app/vmselect/prometheus/export.qtpl:135
+}
 
-//line app/vmselect/prometheus/export.qtpl:147
+//line app/vmselect/prometheus/export.qtpl:137
-		for bb := range resultsCh {
+func StreamExportPromAPIFooter(qw422016 *qt422016.Writer, qt *querytracer.Tracer) {
-//line app/vmselect/prometheus/export.qtpl:147
+//line app/vmselect/prometheus/export.qtpl:137
-			qw422016.N().S(`,`)
-//line app/vmselect/prometheus/export.qtpl:148
-			qw422016.N().Z(bb.B)
-//line app/vmselect/prometheus/export.qtpl:150
-			lines++
-			bytesTotal += len(bb.B)
-			quicktemplate.ReleaseByteBuffer(bb)
-
-//line app/vmselect/prometheus/export.qtpl:154
-		}
-//line app/vmselect/prometheus/export.qtpl:155
-	}
-//line app/vmselect/prometheus/export.qtpl:155
 	qw422016.N().S(`]}`)
-//line app/vmselect/prometheus/export.qtpl:159
+//line app/vmselect/prometheus/export.qtpl:141
-	qt.Donef("export format=promapi: lines=%d, bytes=%d", lines, bytesTotal)
+	qt.Donef("export format=promapi")
 
-//line app/vmselect/prometheus/export.qtpl:161
+//line app/vmselect/prometheus/export.qtpl:143
 	streamdumpQueryTrace(qw422016, qt)
-//line app/vmselect/prometheus/export.qtpl:161
+//line app/vmselect/prometheus/export.qtpl:143
 	qw422016.N().S(`}`)
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 }
 
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
-func WriteExportPromAPIResponse(qq422016 qtio422016.Writer, resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) {
+func WriteExportPromAPIFooter(qq422016 qtio422016.Writer, qt *querytracer.Tracer) {
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 	qw422016 := qt422016.AcquireWriter(qq422016)
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
-	StreamExportPromAPIResponse(qw422016, resultsCh, qt)
+	StreamExportPromAPIFooter(qw422016, qt)
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 	qt422016.ReleaseWriter(qw422016)
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 }
 
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
-func ExportPromAPIResponse(resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) string {
+func ExportPromAPIFooter(qt *querytracer.Tracer) string {
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 	qb422016 := qt422016.AcquireByteBuffer()
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
-	WriteExportPromAPIResponse(qb422016, resultsCh, qt)
+	WriteExportPromAPIFooter(qb422016, qt)
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 	qs422016 := string(qb422016.B)
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 	qt422016.ReleaseByteBuffer(qb422016)
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 	return qs422016
-//line app/vmselect/prometheus/export.qtpl:163
+//line app/vmselect/prometheus/export.qtpl:145
 }
 
-//line app/vmselect/prometheus/export.qtpl:165
+//line app/vmselect/prometheus/export.qtpl:147
-func StreamExportStdResponse(qw422016 *qt422016.Writer, resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) {
-//line app/vmselect/prometheus/export.qtpl:166
-	for bb := range resultsCh {
-//line app/vmselect/prometheus/export.qtpl:167
-		qw422016.N().Z(bb.B)
-//line app/vmselect/prometheus/export.qtpl:168
-		quicktemplate.ReleaseByteBuffer(bb)
-
-//line app/vmselect/prometheus/export.qtpl:169
-	}
-//line app/vmselect/prometheus/export.qtpl:170
-}
-
-//line app/vmselect/prometheus/export.qtpl:170
-func WriteExportStdResponse(qq422016 qtio422016.Writer, resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) {
-//line app/vmselect/prometheus/export.qtpl:170
-	qw422016 := qt422016.AcquireWriter(qq422016)
-//line app/vmselect/prometheus/export.qtpl:170
-	StreamExportStdResponse(qw422016, resultsCh, qt)
-//line app/vmselect/prometheus/export.qtpl:170
-	qt422016.ReleaseWriter(qw422016)
-//line app/vmselect/prometheus/export.qtpl:170
-}
-
-//line app/vmselect/prometheus/export.qtpl:170
-func ExportStdResponse(resultsCh <-chan *quicktemplate.ByteBuffer, qt *querytracer.Tracer) string {
-//line app/vmselect/prometheus/export.qtpl:170
-	qb422016 := qt422016.AcquireByteBuffer()
-//line app/vmselect/prometheus/export.qtpl:170
-	WriteExportStdResponse(qb422016, resultsCh, qt)
-//line app/vmselect/prometheus/export.qtpl:170
-	qs422016 := string(qb422016.B)
-//line app/vmselect/prometheus/export.qtpl:170
-	qt422016.ReleaseByteBuffer(qb422016)
-//line app/vmselect/prometheus/export.qtpl:170
-	return qs422016
-//line app/vmselect/prometheus/export.qtpl:170
-}
-
-//line app/vmselect/prometheus/export.qtpl:172
 func streamprometheusMetricName(qw422016 *qt422016.Writer, mn *storage.MetricName) {
-//line app/vmselect/prometheus/export.qtpl:173
+//line app/vmselect/prometheus/export.qtpl:148
 	qw422016.N().Z(mn.MetricGroup)
-//line app/vmselect/prometheus/export.qtpl:174
+//line app/vmselect/prometheus/export.qtpl:149
 	if len(mn.Tags) > 0 {
-//line app/vmselect/prometheus/export.qtpl:174
+//line app/vmselect/prometheus/export.qtpl:149
 		qw422016.N().S(`{`)
-//line app/vmselect/prometheus/export.qtpl:176
+//line app/vmselect/prometheus/export.qtpl:151
 		tags := mn.Tags
 
-//line app/vmselect/prometheus/export.qtpl:177
+//line app/vmselect/prometheus/export.qtpl:152
 		qw422016.N().Z(tags[0].Key)
-//line app/vmselect/prometheus/export.qtpl:177
+//line app/vmselect/prometheus/export.qtpl:152
 		qw422016.N().S(`=`)
-//line app/vmselect/prometheus/export.qtpl:177
+//line app/vmselect/prometheus/export.qtpl:152
 		qw422016.N().QZ(tags[0].Value)
-//line app/vmselect/prometheus/export.qtpl:178
+//line app/vmselect/prometheus/export.qtpl:153
 		tags = tags[1:]
 
-//line app/vmselect/prometheus/export.qtpl:179
+//line app/vmselect/prometheus/export.qtpl:154
 		for i := range tags {
-//line app/vmselect/prometheus/export.qtpl:180
+//line app/vmselect/prometheus/export.qtpl:155
 			tag := &tags[i]
 
-//line app/vmselect/prometheus/export.qtpl:180
+//line app/vmselect/prometheus/export.qtpl:155
 			qw422016.N().S(`,`)
-//line app/vmselect/prometheus/export.qtpl:181
+//line app/vmselect/prometheus/export.qtpl:156
 			qw422016.N().Z(tag.Key)
-//line app/vmselect/prometheus/export.qtpl:181
+//line app/vmselect/prometheus/export.qtpl:156
 			qw422016.N().S(`=`)
-//line app/vmselect/prometheus/export.qtpl:181
+//line app/vmselect/prometheus/export.qtpl:156
 			qw422016.N().QZ(tag.Value)
-//line app/vmselect/prometheus/export.qtpl:182
+//line app/vmselect/prometheus/export.qtpl:157
 		}
-//line app/vmselect/prometheus/export.qtpl:182
+//line app/vmselect/prometheus/export.qtpl:157
 		qw422016.N().S(`}`)
-//line app/vmselect/prometheus/export.qtpl:184
+//line app/vmselect/prometheus/export.qtpl:159
 	}
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 }
 
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 func writeprometheusMetricName(qq422016 qtio422016.Writer, mn *storage.MetricName) {
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	qw422016 := qt422016.AcquireWriter(qq422016)
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	streamprometheusMetricName(qw422016, mn)
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	qt422016.ReleaseWriter(qw422016)
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 }
 
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 func prometheusMetricName(mn *storage.MetricName) string {
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	qb422016 := qt422016.AcquireByteBuffer()
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	writeprometheusMetricName(qb422016, mn)
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	qs422016 := string(qb422016.B)
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	qt422016.ReleaseByteBuffer(qb422016)
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 	return qs422016
-//line app/vmselect/prometheus/export.qtpl:185
+//line app/vmselect/prometheus/export.qtpl:160
 }

app/vmselect/prometheus/prometheus.go

@@ -6,9 +6,11 @@ import (
 	"math"
 	"net"
 	"net/http"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/bufferedwriter"
@@ -18,7 +20,6 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vmselect/searchutils"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/auth"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
-	"github.com/VictoriaMetrics/VictoriaMetrics/lib/cgroup"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/fasttime"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/flagutil"
@@ -28,7 +29,6 @@ import (
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
 	"github.com/VictoriaMetrics/metrics"
 	"github.com/valyala/fastjson/fastfloat"
-	"github.com/valyala/quicktemplate"
 )
 
 var (
@@ -92,37 +92,19 @@ func FederateHandler(startTime time.Time, at *auth.Token, w http.ResponseWriter,
 	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 	bw := bufferedwriter.Get(w)
 	defer bufferedwriter.Put(bw)
-	var m sync.Map
+	sw := newScalableWriter(bw)
 	err = rss.RunParallel(nil, func(rs *netstorage.Result, workerID uint) error {
 		if err := bw.Error(); err != nil {
 			return err
 		}
-		v, ok := m.Load(workerID)
+		bb := sw.getBuffer(workerID)
-		if !ok {
-			v = &bytesutil.ByteBuffer{}
-			m.Store(workerID, v)
-		}
-		bb := v.(*bytesutil.ByteBuffer)
 		WriteFederate(bb, rs)
-		if len(bb.B) < 1024*1024 {
+		return sw.maybeFlushBuffer(bb)
-			return nil
-		}
-		_, err := bw.Write(bb.B)
-		bb.Reset()
-		return err
 	})
 	if err != nil {
 		return fmt.Errorf("error during sending data to remote client: %w", err)
 	}
-	m.Range(func(k, v interface{}) bool {
+	return sw.flush()
-		bb := v.(*bytesutil.ByteBuffer)
-		_, err := bw.Write(bb.B)
-		return err == nil
-	})
-	if err := bw.Flush(); err != nil {
-		return err
-	}
-	return nil
 }
 
 var federateDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/federate"}`)
@@ -147,15 +129,14 @@ func ExportCSVHandler(startTime time.Time, at *auth.Token, w http.ResponseWriter
 	w.Header().Set("Content-Type", "text/csv; charset=utf-8")
 	bw := bufferedwriter.Get(w)
 	defer bufferedwriter.Put(bw)
-
+	sw := newScalableWriter(bw)
-	resultsCh := make(chan *quicktemplate.ByteBuffer, cgroup.AvailableCPUs())
+	writeCSVLine := func(xb *exportBlock, workerID uint) error {
-	writeCSVLine := func(xb *exportBlock) {
 		if len(xb.timestamps) == 0 {
-			return
+			return nil
 		}
-		bb := quicktemplate.AcquireByteBuffer()
+		bb := sw.getBuffer(workerID)
 		WriteExportCSVLine(bb, xb, fieldNames)
-		resultsCh <- bb
+		return sw.maybeFlushBuffer(bb)
 	}
 	doneCh := make(chan error, 1)
 	if !reduceMemUsage {
@@ -175,17 +156,18 @@ func ExportCSVHandler(startTime time.Time, at *auth.Token, w http.ResponseWriter
 				xb.mn = &rs.MetricName
 				xb.timestamps = rs.Timestamps
 				xb.values = rs.Values
-				writeCSVLine(xb)
+				if err := writeCSVLine(xb, workerID); err != nil {
+					return err
+				}
 				xb.reset()
 				exportBlockPool.Put(xb)
 				return nil
 			})
-			close(resultsCh)
 			doneCh <- err
 		}()
 	} else {
 		go func() {
-			err := netstorage.ExportBlocks(nil, sq, cp.deadline, func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange) error {
+			err := netstorage.ExportBlocks(nil, sq, cp.deadline, func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange, workerID uint) error {
 				if err := bw.Error(); err != nil {
 					return err
 				}
@@ -195,29 +177,21 @@ func ExportCSVHandler(startTime time.Time, at *auth.Token, w http.ResponseWriter
 				xb := exportBlockPool.Get().(*exportBlock)
 				xb.mn = mn
 				xb.timestamps, xb.values = b.AppendRowsWithTimeRangeFilter(xb.timestamps[:0], xb.values[:0], tr)
-				writeCSVLine(xb)
+				if err := writeCSVLine(xb, workerID); err != nil {
+					return err
+				}
 				xb.reset()
 				exportBlockPool.Put(xb)
 				return nil
 			})
-			close(resultsCh)
 			doneCh <- err
 		}()
 	}
-	// Consume all the data from resultsCh.
-	for bb := range resultsCh {
-		// Do not check for error in bw.Write, since this error is checked inside netstorage.ExportBlocks above.
-		_, _ = bw.Write(bb.B)
-		quicktemplate.ReleaseByteBuffer(bb)
-	}
-	if err := bw.Flush(); err != nil {
-		return err
-	}
 	err = <-doneCh
 	if err != nil {
 		return fmt.Errorf("error during sending the exported csv data to remote client: %w", err)
 	}
-	return nil
+	return sw.flush()
 }
 
 var exportCSVDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/api/v1/export/csv"}`)
@@ -235,6 +209,7 @@ func ExportNativeHandler(startTime time.Time, at *auth.Token, w http.ResponseWri
 	w.Header().Set("Content-Type", "VictoriaMetrics/native")
 	bw := bufferedwriter.Get(w)
 	defer bufferedwriter.Put(bw)
+	sw := newScalableWriter(bw)
 
 	// Marshal tr
 	trBuf := make([]byte, 0, 16)
@@ -243,13 +218,13 @@ func ExportNativeHandler(startTime time.Time, at *auth.Token, w http.ResponseWri
 	_, _ = bw.Write(trBuf)
 
 	// Marshal native blocks.
-	err = netstorage.ExportBlocks(nil, sq, cp.deadline, func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange) error {
+	err = netstorage.ExportBlocks(nil, sq, cp.deadline, func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange, workerID uint) error {
 		if err := bw.Error(); err != nil {
 			return err
 		}
-		dstBuf := bbPool.Get()
+		bb := sw.getBuffer(workerID)
+		dst := bb.B
 		tmpBuf := bbPool.Get()
-		dst := dstBuf.B
 		tmp := tmpBuf.B
 
 		// Marshal mn
@@ -265,19 +240,13 @@ func ExportNativeHandler(startTime time.Time, at *auth.Token, w http.ResponseWri
 		tmpBuf.B = tmp
 		bbPool.Put(tmpBuf)
 
-		_, err := bw.Write(dst)
+		bb.B = dst
-
+		return sw.maybeFlushBuffer(bb)
-		dstBuf.B = dst
-		bbPool.Put(dstBuf)
-		return err
 	})
 	if err != nil {
 		return fmt.Errorf("error during sending native data to remote client: %w", err)
 	}
-	if err := bw.Flush(); err != nil {
+	return sw.flush()
-		return fmt.Errorf("error during flushing native data to remote client: %w", err)
-	}
-	return nil
 }
 
 var exportNativeDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/api/v1/export/native"}`)
@@ -304,31 +273,48 @@ func ExportHandler(startTime time.Time, at *auth.Token, w http.ResponseWriter, r
 var exportDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/api/v1/export"}`)
 
 func exportHandler(qt *querytracer.Tracer, at *auth.Token, w http.ResponseWriter, cp *commonParams, format string, maxRowsPerLine int, reduceMemUsage bool) error {
-	writeResponseFunc := WriteExportStdResponse
+	bw := bufferedwriter.Get(w)
-	writeLineFunc := func(xb *exportBlock, resultsCh chan<- *quicktemplate.ByteBuffer) {
+	defer bufferedwriter.Put(bw)
-		bb := quicktemplate.AcquireByteBuffer()
+	sw := newScalableWriter(bw)
+	writeLineFunc := func(xb *exportBlock, workerID uint) error {
+		bb := sw.getBuffer(workerID)
 		WriteExportJSONLine(bb, xb)
-		resultsCh <- bb
+		return sw.maybeFlushBuffer(bb)
 	}
 	contentType := "application/stream+json; charset=utf-8"
 	if format == "prometheus" {
 		contentType = "text/plain; charset=utf-8"
-		writeLineFunc = func(xb *exportBlock, resultsCh chan<- *quicktemplate.ByteBuffer) {
+		writeLineFunc = func(xb *exportBlock, workerID uint) error {
-			bb := quicktemplate.AcquireByteBuffer()
+			bb := sw.getBuffer(workerID)
 			WriteExportPrometheusLine(bb, xb)
-			resultsCh <- bb
+			return sw.maybeFlushBuffer(bb)
 		}
 	} else if format == "promapi" {
-		writeResponseFunc = WriteExportPromAPIResponse
+		WriteExportPromAPIHeader(bw)
-		writeLineFunc = func(xb *exportBlock, resultsCh chan<- *quicktemplate.ByteBuffer) {
+		firstLineOnce := uint32(0)
-			bb := quicktemplate.AcquireByteBuffer()
+		firstLineSent := uint32(0)
+		writeLineFunc = func(xb *exportBlock, workerID uint) error {
+			bb := sw.getBuffer(workerID)
+			if atomic.CompareAndSwapUint32(&firstLineOnce, 0, 1) {
+				// Send the first line to sw.bw
+				WriteExportPromAPILine(bb, xb)
+				_, err := sw.bw.Write(bb.B)
+				bb.Reset()
+				atomic.StoreUint32(&firstLineSent, 1)
+				return err
+			}
+			for atomic.LoadUint32(&firstLineSent) == 0 {
+				// Busy wait until the first line is sent to sw.bw
+				runtime.Gosched()
+			}
+			bb.B = append(bb.B, ',')
 			WriteExportPromAPILine(bb, xb)
-			resultsCh <- bb
+			return sw.maybeFlushBuffer(bb)
 		}
 	}
 	if maxRowsPerLine > 0 {
 		writeLineFuncOrig := writeLineFunc
-		writeLineFunc = func(xb *exportBlock, resultsCh chan<- *quicktemplate.ByteBuffer) {
+		writeLineFunc = func(xb *exportBlock, workerID uint) error {
 			valuesOrig := xb.values
 			timestampsOrig := xb.timestamps
 			values := valuesOrig
@@ -349,19 +335,19 @@ func exportHandler(qt *querytracer.Tracer, at *auth.Token, w http.ResponseWriter
 				}
 				xb.values = valuesChunk
 				xb.timestamps = timestampsChunk
-				writeLineFuncOrig(xb, resultsCh)
+				if err := writeLineFuncOrig(xb, workerID); err != nil {
+					return err
+				}
 			}
 			xb.values = valuesOrig
 			xb.timestamps = timestampsOrig
+			return nil
 		}
 	}
 
 	sq := storage.NewSearchQuery(at.AccountID, at.ProjectID, cp.start, cp.end, cp.filterss, *maxExportSeries)
 	w.Header().Set("Content-Type", contentType)
-	bw := bufferedwriter.Get(w)
-	defer bufferedwriter.Put(bw)
 
-	resultsCh := make(chan *quicktemplate.ByteBuffer, cgroup.AvailableCPUs())
 	doneCh := make(chan error, 1)
 	if !reduceMemUsage {
 		// Unconditionally deny partial response for the exported data,
@@ -381,19 +367,20 @@ func exportHandler(qt *querytracer.Tracer, at *auth.Token, w http.ResponseWriter
 				xb.mn = &rs.MetricName
 				xb.timestamps = rs.Timestamps
 				xb.values = rs.Values
-				writeLineFunc(xb, resultsCh)
+				if err := writeLineFunc(xb, workerID); err != nil {
+					return err
+				}
 				xb.reset()
 				exportBlockPool.Put(xb)
 				return nil
 			})
 			qtChild.Done()
-			close(resultsCh)
 			doneCh <- err
 		}()
 	} else {
 		qtChild := qt.NewChild("background export format=%s", format)
 		go func() {
-			err := netstorage.ExportBlocks(qtChild, sq, cp.deadline, func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange) error {
+			err := netstorage.ExportBlocks(qtChild, sq, cp.deadline, func(mn *storage.MetricName, b *storage.Block, tr storage.TimeRange, workerID uint) error {
 				if err := bw.Error(); err != nil {
 					return err
 				}
@@ -404,26 +391,30 @@ func exportHandler(qt *querytracer.Tracer, at *auth.Token, w http.ResponseWriter
 				xb.mn = mn
 				xb.timestamps, xb.values = b.AppendRowsWithTimeRangeFilter(xb.timestamps[:0], xb.values[:0], tr)
 				if len(xb.timestamps) > 0 {
-					writeLineFunc(xb, resultsCh)
+					if err := writeLineFunc(xb, workerID); err != nil {
+						return err
+					}
 				}
 				xb.reset()
 				exportBlockPool.Put(xb)
 				return nil
 			})
 			qtChild.Done()
-			close(resultsCh)
 			doneCh <- err
 		}()
 	}
-
-	// writeResponseFunc must consume all the data from resultsCh.
-	writeResponseFunc(bw, resultsCh, qt)
-	if err := bw.Flush(); err != nil {
-		return err
-	}
 	err := <-doneCh
 	if err != nil {
-		return fmt.Errorf("error during sending the data to remote client: %w", err)
+		return fmt.Errorf("cannot send data to remote client: %w", err)
+	}
+	if err := sw.flush(); err != nil {
+		return fmt.Errorf("cannot send data to remote client: %w", err)
+	}
+	if format == "promapi" {
+		WriteExportPromAPIFooter(bw, qt)
+	}
+	if err := bw.Flush(); err != nil {
+		return err
 	}
 	return nil
 }
@@ -1212,3 +1203,41 @@ func getCommonParams(r *http.Request, startTime time.Time, requireNonEmptyMatch
 	}
 	return cp, nil
 }
+
+type scalableWriter struct {
+	bw *bufferedwriter.Writer
+	m  sync.Map
+}
+
+func newScalableWriter(bw *bufferedwriter.Writer) *scalableWriter {
+	return &scalableWriter{
+		bw: bw,
+	}
+}
+
+func (sw *scalableWriter) getBuffer(workerID uint) *bytesutil.ByteBuffer {
+	v, ok := sw.m.Load(workerID)
+	if !ok {
+		v = &bytesutil.ByteBuffer{}
+		sw.m.Store(workerID, v)
+	}
+	return v.(*bytesutil.ByteBuffer)
+}
+
+func (sw *scalableWriter) maybeFlushBuffer(bb *bytesutil.ByteBuffer) error {
+	if len(bb.B) < 1024*1024 {
+		return nil
+	}
+	_, err := sw.bw.Write(bb.B)
+	bb.Reset()
+	return err
+}
+
+func (sw *scalableWriter) flush() error {
+	sw.m.Range(func(k, v interface{}) bool {
+		bb := v.(*bytesutil.ByteBuffer)
+		_, err := sw.bw.Write(bb.B)
+		return err == nil
+	})
+	return sw.bw.Flush()
+}

docs/CHANGELOG.md

@@ -27,6 +27,7 @@ See [these docs](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#m
 * FEATURE: [VictoriaMetrics cluster](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html): support specifying tenant ids via `vm_account_id` and `vm_project_id` labels. See [these docs](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#multitenancy-via-labels) and [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2970).
 * FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): improve [relabeling](https://docs.victoriametrics.com/vmagent.html#relabeling) performance by up to 3x for non-trivial `regex` values such as `([^:]+):.+`, which can be used for extracting a `host` part from `host:port` label value.
 * FEATURE: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): improve performance by up to 4x for queries containing non-trivial `regex` filters such as `{path=~"/foo/.+|/bar"}`.
+* FEATURE: improve performance scalability on systems with many CPU cores for [/federate](https://docs.victoriametrics.com/#federation) and [/api/v1/export/...](https://docs.victoriametrics.com/#how-to-export-time-series) endpoints.
 * FEATURE: sanitize metric names for data ingested via [DataDog protocol](https://docs.victoriametrics.com/#how-to-send-data-from-datadog-agent) according to [DataDog metric naming](https://docs.datadoghq.com/metrics/custom_metrics/#naming-custom-metrics). The behaviour can be disabled by passing `-datadog.sanitizeMetricName=false` command-line flag. Thanks to @PerGon for [the pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/3105).
 * FEATURE: add `-usePromCompatibleNaming` command-line flag to [vmagent](https://docs.victoriametrics.com/vmagent.html), to single-node VictoriaMetrics and to `vminsert` component of VictoriaMetrics cluster. This flag can be used for normalizing the ingested metric names and label names to [Prometheus-compatible form](https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels). If this flag is set, then all the chars unsupported by Prometheus are replaced with `_` chars in metric names and labels of the ingested samples. See [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3113).
 * FEATURE: accept whitespace in metric names and tags ingested via [Graphite plaintext protocol](https://docs.victoriametrics.com/#how-to-send-data-from-graphite-compatible-agents-such-as-statsd) according to [the specs](https://graphite.readthedocs.io/en/latest/tags.html). See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3102).