[jira] [Commented] (CASSANDRA-3578) Multithreaded commitlog

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-3578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13773408#comment-13773408 ] 

Jonathan Ellis commented on CASSANDRA-3578:
-------------------------------------------

I've seen several cases of nodes failing to keep up with write requests where the commitlog was the bottleneck.  These were all workloads throwing MB-sized columns around.  Granted, that's not exactly our bread and butter.
                
> Multithreaded commitlog
> -----------------------
>
>                 Key: CASSANDRA-3578
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3578
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Priority: Minor
>         Attachments: 0001-CASSANDRA-3578.patch, 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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