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receive: reduce allocations with buffer pooling and enforce streaming size limits #287

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f9f4eb6
memory heap optimizations
mkusumdb Jan 27, 2026
237f527
with unit test fixes
mkusumdb Jan 28, 2026
da4deec
fix test
mkusumdb Jan 30, 2026
6081842
Fix tenant extraction fallback and update test expectations
mkusumdb Feb 3, 2026
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67 changes: 57 additions & 10 deletions pkg/receive/handler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,26 @@ var (
errNotReady = errors.New("target not ready")
errUnavailable = errors.New("target not available")
errInternal = errors.New("internal error")

// Buffer pools to reduce memory allocations in hot path.
compressedBufPool = sync.Pool{
New: func() interface{} {
return bytes.NewBuffer(make([]byte, 0, 32*1024)) // 32KB default
},
}

decompressedBufPool = sync.Pool{
New: func() interface{} {
buf := make([]byte, 0, 128*1024) // 128KB default
return &buf
},
}

writeRequestPool = sync.Pool{
New: func() interface{} {
return &prompb.WriteRequest{}
},
}
)

type WriteableStoreAsyncClient interface {
Expand Down Expand Up @@ -564,7 +584,13 @@ func (h *Handler) receiveHTTP(w http.ResponseWriter, r *http.Request) {
requestLimiter := h.Limiter.RequestLimiter()
// io.ReadAll dynamically adjust the byte slice for read data, starting from 512B.
// Since this is receive hot path, grow upfront saving allocations and CPU time.
compressed := bytes.Buffer{}
// Use buffer pool to reduce allocations.
compressed := compressedBufPool.Get().(*bytes.Buffer)
defer func() {
compressed.Reset()
compressedBufPool.Put(compressed)
}()

if r.ContentLength >= 0 {
if !requestLimiter.AllowSizeBytes(tenantHTTP, r.ContentLength) {
http.Error(w, "write request too large", http.StatusRequestEntityTooLarge)
Expand All @@ -574,28 +600,40 @@ func (h *Handler) receiveHTTP(w http.ResponseWriter, r *http.Request) {
} else {
compressed.Grow(512)
}
_, err = io.Copy(&compressed, r.Body)
_, err = io.Copy(compressed, r.Body)
if err != nil {
http.Error(w, errors.Wrap(err, "read compressed request body").Error(), http.StatusInternalServerError)
return
}
reqBuf, err := s2.Decode(nil, compressed.Bytes())

// Use buffer pool for decompressed data.
reqBuf := decompressedBufPool.Get().(*[]byte)
defer decompressedBufPool.Put(reqBuf)
*reqBuf, err = s2.Decode((*reqBuf)[:0], compressed.Bytes())
if err != nil {
level.Error(tLogger).Log("msg", "snappy decode error", "err", err)
http.Error(w, errors.Wrap(err, "snappy decode error").Error(), http.StatusBadRequest)
return
}

if !requestLimiter.AllowSizeBytes(tenantHTTP, int64(len(reqBuf))) {
if !requestLimiter.AllowSizeBytes(tenantHTTP, int64(len(*reqBuf))) {
http.Error(w, "write request too large", http.StatusRequestEntityTooLarge)
return
}

// NOTE: Due to zero copy ZLabels, Labels used from WriteRequests keeps memory
// from the whole request. Ensure that we always copy those when we want to
// store them for longer time.
var wreq prompb.WriteRequest
if err := proto.Unmarshal(reqBuf, &wreq); err != nil {
// Use proto message pool to reduce allocations.
wreq := writeRequestPool.Get().(*prompb.WriteRequest)
wreq.Reset() // Reset immediately after getting from pool
defer func() {
// Reset before returning to pool to avoid memory leaks.
wreq.Reset()
writeRequestPool.Put(wreq)
}()

if err := proto.Unmarshal(*reqBuf, wreq); err != nil {
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
Expand Down Expand Up @@ -637,14 +675,24 @@ func (h *Handler) receiveHTTP(w http.ResponseWriter, r *http.Request) {
}

// Apply relabeling configs.
h.relabel(&wreq)
h.relabel(wreq)
if len(wreq.Timeseries) == 0 {
level.Debug(tLogger).Log("msg", "remote write request dropped due to relabeling.")
return
}

// Deep copy all labels to detach them from the pooled buffer.
// This is necessary because:
// 1. The pooled buffer will be returned and reused when this function returns
// 2. Async remote write goroutines may still reference the labels
// 3. Even local writes need detached labels for TSDB storage
// Use the same intern setting as the writer to ensure consistent behavior.
for i := range wreq.Timeseries {
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@yuchen-db yuchen-db Feb 3, 2026

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nit: we might want to do the same for exemplars as well

labelpb.ReAllocZLabelsStrings(&wreq.Timeseries[i].Labels, h.writer.opts.Intern)
}

responseStatusCode := http.StatusOK
tenantStats, err := h.handleRequest(ctx, rep, tenantHTTP, &wreq)
tenantStats, err := h.handleRequest(ctx, rep, tenantHTTP, wreq)
if err != nil {
level.Debug(tLogger).Log("msg", "failed to handle request", "err", err.Error())
switch errors.Cause(err) {
Expand Down Expand Up @@ -930,9 +978,8 @@ func (h *Handler) distributeTimeseriesToReplicas(
tenantLabel := lbls.Get(h.splitTenantLabelName)
if tenantLabel != "" {
tenant = h.splitTenantLabelName + ":" + tenantLabel
} else {
tenant = h.options.DefaultTenantID
}
// If label not found, keep using tenantHTTP (don't override)
}

for _, rn := range replicas {
Expand Down
10 changes: 5 additions & 5 deletions test/e2e/receive_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1052,8 +1052,8 @@ func TestReceiveExtractsTenant(t *testing.T) {
Timeseries: []prompb.TimeSeries{
{
Labels: []prompb.Label{
{Name: tenantLabelName, Value: "tenant-1"},
{Name: "aa", Value: "bb"},
{Name: tenantLabelName, Value: "tenant-1"},
},
Samples: []prompb.Sample{
{Value: 1, Timestamp: time.Now().UnixMilli()},
Expand All @@ -1063,7 +1063,7 @@ func TestReceiveExtractsTenant(t *testing.T) {
})
}))

testutil.Ok(t, i.WaitSumMetricsWithOptions(e2emon.Equals(0), []string{"prometheus_tsdb_blocks_loaded"}, e2emon.WithLabelMatchers(matchers.MustNewMatcher(matchers.MatchEqual, "tenant", "tenant-1")), e2emon.WaitMissingMetrics()))
testutil.Ok(t, i.WaitSumMetricsWithOptions(e2emon.Equals(0), []string{"prometheus_tsdb_blocks_loaded"}, e2emon.WithLabelMatchers(matchers.MustNewMatcher(matchers.MatchEqual, "tenant", tenantLabelName+":tenant-1")), e2emon.WaitMissingMetrics()))
})

t.Run("tenant label is extracted from one series, default is used for the other one", func(t *testing.T) {
Expand All @@ -1072,8 +1072,8 @@ func TestReceiveExtractsTenant(t *testing.T) {
Timeseries: []prompb.TimeSeries{
{
Labels: []prompb.Label{
{Name: tenantLabelName, Value: "tenant-2"},
{Name: "aa", Value: "bb"},
{Name: tenantLabelName, Value: "tenant-2"},
},
Samples: []prompb.Sample{
{Value: 1, Timestamp: time.Now().UnixMilli()},
Expand Down Expand Up @@ -1101,8 +1101,8 @@ func TestReceiveExtractsTenant(t *testing.T) {
Timeseries: []prompb.TimeSeries{
{
Labels: []prompb.Label{
{Name: tenantLabelName, Value: "tenant-3"},
{Name: "aa", Value: "bb"},
{Name: tenantLabelName, Value: "tenant-3"},
},
Samples: []prompb.Sample{
{Value: 1, Timestamp: time.Now().UnixMilli()},
Expand Down Expand Up @@ -1149,7 +1149,7 @@ func TestReceiveExtractsTenant(t *testing.T) {
}))

testutil.Ok(t, i.WaitSumMetricsWithOptions(e2emon.Equals(0), []string{"prometheus_tsdb_blocks_loaded"}, e2emon.WithLabelMatchers(matchers.MustNewMatcher(matchers.MatchEqual, "tenant", "http-tenant")), e2emon.WaitMissingMetrics()))
testutil.Ok(t, i.WaitSumMetricsWithOptions(e2emon.Equals(0), []string{"prometheus_tsdb_blocks_loaded"}, e2emon.WithLabelMatchers(matchers.MustNewMatcher(matchers.MatchEqual, "tenant", "tenant-3")), e2emon.WaitMissingMetrics()))
testutil.Ok(t, i.WaitSumMetricsWithOptions(e2emon.Equals(0), []string{"prometheus_tsdb_blocks_loaded"}, e2emon.WithLabelMatchers(matchers.MustNewMatcher(matchers.MatchEqual, "tenant", tenantLabelName+":tenant-3")), e2emon.WaitMissingMetrics()))

})
}
Expand Down
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