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https://issues.apache.org/jira/browse/CASSANDRA-16072?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17185047#comment-17185047
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Michael Semb Wever edited comment on CASSANDRA-16072 at 8/26/20, 9:08 AM:
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[~Bereng], ways {{(prev + size)}} could wrap around…
- prev itself has wrapped around, the method still then returns negative,
- {{`prev > endOfBuffer`}} and {{`prev + size > Integer.MAX_VALUE`}}.
In the later, {{`endOfBuffer + size> Integer.MAX_VALUE`}} must also be true, so
it would be when {{commitlog_segment_size_in_mb}} is set to some value close
(relative to the size of mutations) to 2GB.
To prevent this would it be enough to
{code}if (((long)prev + size) >= endOfBuffer){code}
was (Author: michaelsembwever):
[~Bereng], ways {{(prev + size)}} could wrap around…
- prev itself has wrapped around, the method still then returns negative,
- {{prev > endOfBuffer}} and {{prev + size > Integer.MAX_VALUE}}.
In the later, {{endOfBuffer + size> Integer.MAX_VALUE}} must also be true, so
it would be when commitlog_segment_size_in_mb is set to some value close
(relative to the size of mutations) to 2GB.
To prevent this would it be enough to
{code}if (((long)prev + size) >= endOfBuffer){code}
> 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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