Finer concurrency in 'MetricType.observe' / 'MetricType.collect' #59
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avolokhov
changed the title
ktoso
reviewed
Aug 23, 2021
| return histogram | ||
| } else { | ||
| let newHistogram = PromHistogram<T, U>(histogram.name, histogram.help, labels, Buckets(histogram.upperBounds), self) | ||
| histogram.subHistograms.append(newHistogram) | ||
| guard let prometheus = prometheus else { fatalError("Lingering Histogram") } |
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Hmm can this actually ever happen or just annoyance because that weak there that shoulnd't really manifest in reality?
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Yes, this is a weak reference thing. I think reference to Prometheus is redundant, I'll try to track down its origins and potentially remove if indeed unnecessary.
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Ah i see the error just moved around, it was there before.
ktoso
approved these changes
Aug 23, 2021
| return histogram | ||
| } else { | ||
| let newHistogram = PromHistogram<T, U>(histogram.name, histogram.help, labels, Buckets(histogram.upperBounds), self) | ||
| histogram.subHistograms.append(newHistogram) | ||
| guard let prometheus = prometheus else { fatalError("Lingering Histogram") } |
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Ah i see the error just moved around, it was there before.
| subHistogram.labels.le = "" | ||
| let (buckets, subHistograms, labels) = self.lock.withLock { | ||
| (self.buckets, self.subHistograms, self.labels) | ||
| } |
MrLotU
approved these changes
Aug 24, 2021
Merged
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Every metric type has a lock that's taken for the whole duration of consuming a metric value, and also for the whole duration of observe. This PR puts as much computations out of critical section as we can afford, which results in a significant performance boost.
With these changes,
Lock.withLocktakes only 25% ofPromHistogram.observe, of which half is locking/unlocking and the other half iscollection.filter.Reducing the scope of locking helps bringing
lock.withLockto 50% ofPromHistogram.observe. ChangingsubHistogramsfrom array to map, reduces it further to25%Checklist
Motivation and Context
This PR brings concurrency optimisations that result in better emission latencies.
Description
Every MetricType's lock is now only held during access to corresponding state in a thread safe manner, all computations are moved outside critical section.
subHistograms is now a
Mapinstead of array.