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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3578) Multithreaded commitlog
Date Sun, 01 Dec 2013 00:05:35 GMT

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which I suspect is obsolete although I'm not sure what the effect on tests is.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