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https://issues.apache.org/jira/browse/CASSANDRA-16072?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17301179#comment-17301179
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Michael Semb Wever commented on CASSANDRA-16072:
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bq. The patch breaks the CommitLogSegment's closing process (whether capacity
becomes full, or endOfBuffer gets re-assigned before buffer becomes null).
Investigating this further…
CommitLogSegment depended on the {{compareAndSet}}, to keep {{allocatePosition
< endOfBuffer}}. Given that the atomic add approach isn't applicable to this
code, I have applied the ConstantBackoffCAS algorithm (see CASSANDRA-15922)
here.
Patches
-
[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/482/badge/icon!|https://ci-cassandra.apache.org/blue/organizations/jenkins/Cassandra-devbranch/detail/Cassandra-devbranch/482/pipeline]
-
[trunk|https://github.com/apache/cassandra/compare/trunk...thelastpickle:mck/trunk_cas_improvements]
–
[!https://ci-cassandra.apache.org/job/Cassandra-devbranch/483/badge/icon!|https://ci-cassandra.apache.org/blue/organizations/jenkins/Cassandra-devbranch/detail/Cassandra-devbranch/483/pipeline]
> 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
>
>
> 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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