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[PERF] Remote-write: re-use memory to read WAL data (#16197)

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The `:=` causes new variables to be created, which means the outer
slice stays at nil, and new memory is allocated every time round the
loop.

Extracted from https://github.com/prometheus/prometheus/pull/16182
Credit to @bwplotka.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This commit is contained in:
Bryan Boreham 2025-03-11 10:49:51 +00:00 committed by GitHub
parent 53be282396
commit 30d04792ca
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GPG Key ID: B5690EEEBB952194
1 changed files with 8 additions and 7 deletions
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15
tsdb/wlog/watcher.go
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@ -491,12 +491,13 @@ func (w *Watcher) readSegment(r *LiveReader, segmentNum int, tail bool) error {
metadata []record.RefMetadata
)
for r.Next() && !isClosed(w.quit) {
var err error
rec := r.Record()
w.recordsReadMetric.WithLabelValues(dec.Type(rec).String()).Inc()
switch dec.Type(rec) {
case record.Series:
series, err := dec.Series(rec, series[:0])
series, err = dec.Series(rec, series[:0])
if err != nil {
w.recordDecodeFailsMetric.Inc()
return err
@ -509,7 +510,7 @@ func (w *Watcher) readSegment(r *LiveReader, segmentNum int, tail bool) error {
if !tail {
break
}
samples, err := dec.Samples(rec, samples[:0])
samples, err = dec.Samples(rec, samples[:0])
if err != nil {
w.recordDecodeFailsMetric.Inc()
return err
@ -539,7 +540,7 @@ func (w *Watcher) readSegment(r *LiveReader, segmentNum int, tail bool) error {
if !tail {
break
}
exemplars, err := dec.Exemplars(rec, exemplars[:0])
exemplars, err = dec.Exemplars(rec, exemplars[:0])
if err != nil {
w.recordDecodeFailsMetric.Inc()
return err
@ -554,7 +555,7 @@ func (w *Watcher) readSegment(r *LiveReader, segmentNum int, tail bool) error {
if !tail {
break
}
histograms, err := dec.HistogramSamples(rec, histograms[:0])
histograms, err = dec.HistogramSamples(rec, histograms[:0])
if err != nil {
w.recordDecodeFailsMetric.Inc()
return err
@ -582,7 +583,7 @@ func (w *Watcher) readSegment(r *LiveReader, segmentNum int, tail bool) error {
if !tail {
break
}
floatHistograms, err := dec.FloatHistogramSamples(rec, floatHistograms[:0])
floatHistograms, err = dec.FloatHistogramSamples(rec, floatHistograms[:0])
if err != nil {
w.recordDecodeFailsMetric.Inc()
return err
@ -606,12 +607,12 @@ func (w *Watcher) readSegment(r *LiveReader, segmentNum int, tail bool) error {
if !w.sendMetadata {
break
}
meta, err := dec.Metadata(rec, metadata[:0])
metadata, err = dec.Metadata(rec, metadata[:0])
if err != nil {
w.recordDecodeFailsMetric.Inc()
return err
}
w.writer.StoreMetadata(meta)
w.writer.StoreMetadata(metadata)
case record.Unknown:
// Could be corruption, or reading from a WAL from a newer Prometheus.