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Posted to jira@kafka.apache.org by "Matthias J. Sax (Jira)" <ji...@apache.org> on 2025/10/21 20:15:00 UTC
[jira] [Assigned] (KAFKA-19678) Streams open iterator tracking has high contention on metrics lock
[ https://issues.apache.org/jira/browse/KAFKA-19678?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Matthias J. Sax reassigned KAFKA-19678:
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Assignee: Bill Bejeck
> Streams open iterator tracking has high contention on metrics lock
> ------------------------------------------------------------------
>
> Key: KAFKA-19678
> URL: https://issues.apache.org/jira/browse/KAFKA-19678
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 4.1.0
> Reporter: Steven Schlansker
> Assignee: Bill Bejeck
> Priority: Major
> Attachments: image-2025-09-05-12-13-24-910.png, image-2025-10-20-13-36-54-857.png, image-2025-10-21-09-24-02-505.png
>
>
> We run Kafka Streams 4.1.0 with custom processors that heavily use state store range iterators.
> While investigating disappointing performance, we found a surprising source of lock contention.
> Over the course of about a 1 minute profiler sample, the {{org.apache.kafka.common.metrics.Metrics}} lock is taken approximately 40,000 times and blocks threads for about 1 minute.
> This appears to be because our state stores generally have no iterators open, except when their processor is processing a record, in which case it opens an iterator (taking the lock through {{OpenIterators.add}} into {{{}Metrics.registerMetric{}}}), does a tiny bit of work, and then closes the iterator (again taking the lock through {{OpenIterators.remove}} into {{{}Metrics.removeMetric{}}}).
> So, stream processing threads takes a globally shared lock twice per record, for this subset of our data. I've attached a profiler thread state visualization with our findings - the red bar indicates the thread was blocked during the sample on this lock. As you can see, this lock seems to be severely hampering our performance.
>
> !image-2025-09-05-12-13-24-910.png!
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