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From "Vijay (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-3578) Multithreaded commitlog
Date Fri, 18 Oct 2013 03:03:42 GMT


Vijay commented on CASSANDRA-3578:

Pushed my changes to

* The above takes a different approach, we update commit log as a part of the mutation thread
and no more threads to deal with serialization. CAS operation to reserve a block of bytes
in the MMapped segment (Similar to slab allocator) and activate segments.
* Sync is managed in the separate thread still.
* Doesn't have a end of segment on each mutation, we just have header which will hold the

We could clean up little more if it looks good.
Performance test shows a slight improvements... May be once we remove other bottlenecks the
improvements (also have to test on spinning drives) will be more visible.

> Multithreaded commitlog
> -----------------------
>                 Key: CASSANDRA-3578
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Vijay
>            Priority: Minor
>              Labels: performance
>         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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