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https://issues.apache.org/jira/browse/CASSANDRA-14281?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16390310#comment-16390310
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Chris Lohfink commented on CASSANDRA-14281:
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Is there a reason to not use an array of longadders which keeps the long for
each bucket in a ThreadLocal than recreate the logic to do merging on histogram
level? Would be a smaller change to just change AtomicLong[]s to LongAdder[]
> Reduce contention on DecayingEstimatedHistogramReservoir
> --------------------------------------------------------
>
> Key: CASSANDRA-14281
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14281
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Michael Burman
> Assignee: Michael Burman
> Priority: Major
>
> Currently, the DecayingEstimatedHistogramReservoir acquires a lock for each
> update operation, which causes a contention if there are more than one thread
> updating the histogram. This impacts scalability when using larger machines.
> We should make it lock-free as much as possible and also avoid a single
> CAS-update from blocking all the concurrent threads from making an update.
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