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Vijay commented on CASSANDRA-3578:
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Pushed my changes to https://github.com/Vijay2win/cassandra/commits/3578
* 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 end.
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: https://issues.apache.org/jira/browse/CASSANDRA-3578
> 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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