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https://issues.apache.org/jira/browse/CASSANDRA-19365?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17883674#comment-17883674
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Caleb Rackliffe edited comment on CASSANDRA-19365 at 9/23/24 3:33 AM:
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Attached my CI results, which look good. Let me make a final pass at review
this week. (I'm guessing porting down through to 4.0 won't involve a ton of
changes the trunk patch...)
was (Author: maedhroz):
Attached my CI results, which look good. Let me make a final pass at review
this week.
> invalid EstimatedHistogramReservoirSnapshot::getValue values due to race
> condition in DecayingEstimatedHistogramReservoir
> -------------------------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-19365
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19365
> Project: Cassandra
> Issue Type: Bug
> Components: Observability/Metrics
> Reporter: Jakub Zytka
> Assignee: Maxim Muzafarov
> Priority: Normal
> Fix For: 4.0.x, 4.1.x, 5.0.x, 5.x
>
> Attachments: ci_summary.html, result_details.tar.gz
>
> Time Spent: 3.5h
> Remaining Estimate: 0h
>
> `DecayingEstimatedHistogramReservoir` has a race condition between `update`
> and `rescaleIfNeeded`.
> A sample which ends up (`update`) in an already scaled decayingBucket
> (`rescaleIfNeeded`) may still use a non-scaled weight because `decayLandmark`
> has not been updated yet at the moment of `update`.
>
> The observed consequence was flooding of the cluster with speculative retries
> (we happened to hit low-percentile buckets with overweight samples, which
> drove p99 below true p50 for a long time).
> Please note that despite the manifestation being similar to CASSANDRA-19330,
> these are two distinct bugs in their own right.
> This bug affects versions 4.0+
> On 3.11 there's locking in DEHR. I did not check earlier versions.
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