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https://issues.apache.org/jira/browse/CASSANDRA-3578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13835907#comment-13835907
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Jonathan Ellis commented on CASSANDRA-3578:
-------------------------------------------

bq. Are you referring to the fact that I always use buffer.capacity() instead 
of the constant defining their size?

No, I'm talking about

{code}
            // Map the segment, extending or truncating it to the standard 
segment size
            
logFileAccessor.setLength(DatabaseDescriptor.getCommitLogSegmentSize());
{code}

There's also

{code}
        // check against SEGMENT_SIZE avoids recycling odd-sized or empty 
segments from old C* versions and unit tests
{code}

which I suspect is obsolete although I'm not sure what the effect on tests is.


> Multithreaded commitlog
> -----------------------
>
>                 Key: CASSANDRA-3578
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3578
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Benedict
>            Priority: Minor
>              Labels: performance
>         Attachments: 0001-CASSANDRA-3578.patch, ComitlogStress.java, 
> Current-CL.png, Multi-Threded-CL.png, TestEA.java, latency.svg, oprate.svg, 
> parallel_commit_log_2.patch
>
>
> Brian Aker pointed out a while ago that allowing multiple threads to modify 
> the commitlog simultaneously (reserving space for each with a CAS first, the 
> way we do in the SlabAllocator.Region.allocate) can improve performance, 
> since you're not bottlenecking on a single thread to do all the copying and 
> CRC computation.
> Now that we use mmap'd CommitLog segments (CASSANDRA-3411) this becomes 
> doable.
> (moved from CASSANDRA-622, which was getting a bit muddled.)



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