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From "Michael Semb Wever (Jira)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-16072) Reduce thread contention in CommitLogSegment and HintsBuffer by rewriting CAS loops to atomic adds
Date Thu, 08 Jul 2021 15:51:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-16072?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17377472#comment-17377472
] 

Michael Semb Wever commented on CASSANDRA-16072:
------------------------------------------------

bq. Maybe we want a rebase and new CI runs after so long?

Of course! 

- [3.11|https://github.com/apache/cassandra/compare/cassandra-3.11...thelastpickle:mck/cassandra-3.11_cas_improvements]
[!https://ci-cassandra.apache.org/job/Cassandra-devbranch/904/badge/icon!|https://ci-cassandra.apache.org/job/Cassandra-devbranch/904/]
- [4.0|https://github.com/apache/cassandra/compare/trunk...thelastpickle:mck/cassandra-4.0_cas_improvements]
[!https://ci-cassandra.apache.org/job/Cassandra-devbranch/905/badge/icon!|https://ci-cassandra.apache.org/job/Cassandra-devbranch/905/]
- [trunk|https://github.com/apache/cassandra/compare/trunk...thelastpickle:mck/trunk_cas_improvements]
[!https://ci-cassandra.apache.org/job/Cassandra-devbranch/906/badge/icon!|https://ci-cassandra.apache.org/job/Cassandra-devbranch/906/]

> Reduce thread contention in CommitLogSegment and HintsBuffer by rewriting CAS loops to
atomic adds
> --------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-16072
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-16072
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Consistency/Hints, Local/Commit Log
>            Reporter: Michael Semb Wever
>            Assignee: Michael Semb Wever
>            Priority: Normal
>             Fix For: 3.11.x, 4.0.x, 4.x
>
>
> Follow up to CASSANDRA-15922
> Both CommitLogSegment and HintsBuffer use AtomicIntegers for the current offset when
allocating. Like in CASSANDRA\-15922 the loops on {{.compareAndSet(..)}} can be replaced with
atomic adds using the {{. getAndAdd(..)}} method.
> In highly contended environments the CAS failures can be high, starving writes in a running
Cassandra node. On the same cluster CASSANDRA\-15922 was found, after CASSANDRA\-15922's fix
was deployed, there was still problems around commit log flushing and hints. No flamegraph
was collected that demonstrated the thread contention as clearly as was found in CASSANDRA\-15922,
but the performance fix proposed here hopefully is obvious enough.



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