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https://issues.apache.org/jira/browse/CASSANDRA-16072?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17188321#comment-17188321
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Benjamin Lerer commented on CASSANDRA-16072:
--------------------------------------------
If we do some rough calculation on the limits of things for {{HintBuffer}}:
If the slab size is around {{1GB}}, the maximum hint size will be around
{{500MB}}.
Once we exceed the slab capacity the {{position}} will be set to {{-2GB}}. It
will only take 5 hints at a size close from the maximum hint size to be back on
the positive side.
It seems to me that we are on a risky side. What do you think?
Regarding {{CommitLogSegment}}, it will be good to have a comment explaining
the negative value logic. People might not get it straight away as it is an
obvious way to handle overflow.
> 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-beta
>
>
> 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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