cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-3578) Multithreaded commitlog
Date Fri, 08 Nov 2013 09:30:22 GMT


Benedict commented on CASSANDRA-3578:

bq. We don't guarantee that in PeriodicCommitLogExecutorService

No, you're right. I misspoke. For PeriodicCLE we only don't *commit* anything we cannot later

Unfortunately the BatchCLE in your patch could still ACK messages that weren't replayable,
as a message could reserve space, not finish writing it, and so not get placed on the waitIfNeeded()
call/queue, but a later writer could race past it and get there. Since the earlier writer
hasn't serialized its size, the later message is not replayable. Besides, the queue has *two*
locks, so you'd still have a lock ;-)

> 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,, Current-CL.png,
Multi-Threded-CL.png, 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.)

This message was sent by Atlassian JIRA

View raw message