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https://issues.apache.org/jira/browse/CASSANDRA-3578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13840472#comment-13840472
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Benedict edited comment on CASSANDRA-3578 at 12/5/13 7:39 PM:
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The idea of the % was to give some sense of scale of the problem. The problem
with just offering the average is that it's only averaged over the number of
lagged commits, which doesn't tell the whole story (if most of the commits
didn't lag, it might not be worth worrying about), or averaged over all the
commits which might be overly dismissive because a lot of commits may be
NO-OPs, so giving a ratio of time spent committing to time spent lagged seemed
a useful compromise. Though perhaps simply total time spent lagged and total
time spent committing might be more useful.
was (Author: benedict):
The idea of the % was to give some sense of scale of the problem. The problem
with just offering a count is that it's only averaged over the number of lagged
commits, which doesn't tell the whole story (if most of the commits didn't lag,
it might not be worth worrying about), and averaging over all the commits might
be overly dismissive because a lot of commits may be NO-OPs, so giving a ratio
of time spent committing to time spent lagged seemed a useful compromise.
Though perhaps simply total time spent lagged and total time spent committing
might be more useful.
> 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
> Fix For: 2.1
>
> Attachments: 0001-CASSANDRA-3578.patch, 3578-logging-v2.txt,
> 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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