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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3578) Multithreaded commitlog
Date Sun, 01 Dec 2013 14:20:36 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13836033#comment-13836033
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Jonathan Ellis commented on CASSANDRA-3578:
-------------------------------------------

bq. It is non-blocking in its abstraction which makes it absolutely the correct abstraction
to use here

How is WaitQueue different from using Object.wait/notifyAll?

bq. If we were now to split out the CL.add() into the calling thread instead of the write
stage, returning a Future to wait on in the write stage, we could support max_connection writes
instead, which would be much larger

Well, in the general case of writing to more than just a single local replica, this distinction
isn't really meaningful.  At *some* point you have to do blocking i/o to disk so whether you
call that {{concurrent_writes}} or {{fake_aio_threads}} doesn't really matter.

> 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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