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promql: Fix trigger for HistogramStatsIterator

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PR #16702 introduced a regression because it was too strict in
detecting the condition for using the `HistogramStatsIterator`. It
essentially required the triggering function to be buried at least one
level deep.

`histogram_count(sum(rate(native_histogram_series[2m]))` would not
trigger anymore, but
`1*histogram_count(sum(rate(native_histogram_series[2m]))` would.

Ironically, PR #16682 made the performance of the
`HistogramStatsIterator` so much worse that _not_ using it was often
better, but this has to be addressed in a separate commit.

This commit reinstates the previous `HistogramStatsIterator` detection
behavior, as PR #16702 intended to keep it.

Relevant benchmark changes with this commit (i.e. old is without using
`HistogramStatsIterator`, new is with `HistogramStatsIterator`):

name                                                                       old time/op    new time/op    delta
NativeHistograms/histogram_count_with_short_rate_interval-16                  802ms ± 3%     837ms ± 3%    +4.42%  (p=0.008 n=5+5)
NativeHistograms/histogram_count_with_long_rate_interval-16                   1.22s ± 3%     1.11s ± 1%    -9.46%  (p=0.008 n=5+5)
NativeHistogramsCustomBuckets/histogram_count_with_short_rate_interval-16     611ms ± 5%     751ms ± 6%   +22.87%  (p=0.008 n=5+5)
NativeHistogramsCustomBuckets/histogram_count_with_long_rate_interval-16      975ms ± 4%    1131ms ±11%   +16.04%  (p=0.008 n=5+5)

name                                                                       old alloc/op   new alloc/op   delta
NativeHistograms/histogram_count_with_short_rate_interval-16                  222MB ± 0%     531MB ± 0%  +139.63%  (p=0.008 n=5+5)
NativeHistograms/histogram_count_with_long_rate_interval-16                   323MB ± 0%     528MB ± 0%   +63.81%  (p=0.008 n=5+5)
NativeHistogramsCustomBuckets/histogram_count_with_short_rate_interval-16     179MB ± 0%     452MB ± 0%  +153.07%  (p=0.016 n=4+5)
NativeHistogramsCustomBuckets/histogram_count_with_long_rate_interval-16      175MB ± 0%     452MB ± 0%  +157.73%  (p=0.016 n=4+5)

name                                                                       old allocs/op  new allocs/op  delta
NativeHistograms/histogram_count_with_short_rate_interval-16                  4.48M ± 0%     8.95M ± 0%   +99.51%  (p=0.008 n=5+5)
NativeHistograms/histogram_count_with_long_rate_interval-16                   5.02M ± 0%     8.84M ± 0%   +75.89%  (p=0.008 n=5+5)
NativeHistogramsCustomBuckets/histogram_count_with_short_rate_interval-16     3.00M ± 0%     5.96M ± 0%   +98.93%  (p=0.008 n=5+5)
NativeHistogramsCustomBuckets/histogram_count_with_long_rate_interval-16      2.89M ± 0%     5.86M ± 0%  +102.69%  (p=0.016 n=4+5)

Signed-off-by: beorn7 <beorn@grafana.com>
This commit is contained in:
beorn7 2025-09-02 22:32:36 +02:00
parent 5b153f80a5
commit 87d7c12563
1 changed files with 1 additions and 1 deletions
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2
promql/engine.go
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@ -3891,7 +3891,7 @@ func detectHistogramStatsDecoding(expr parser.Expr) {
return nil
}
for i := len(path) - 1; i > 0; i-- { // Walk backwards up the path.
for i := len(path) - 1; i >= 0; i-- { // Walk backwards up the path.
call, ok := path[i].(*parser.Call)
if !ok {
continue