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https://issues.apache.org/jira/browse/CASSANDRA-3578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13835923#comment-13835923
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Jonathan Ellis edited comment on CASSANDRA-3578 at 12/1/13 2:07 AM:
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bq. We point next to next, which is absolutely correct
I understand what sync is doing; my point is that xxxxSyncMarkerPosition always
points to the *last* offset before which the contents are synced, which we'll
revisit when we sync again / write the next marker (referred to appropriately
as {{nextMarker}} in the code). Your own comments refer to "last" or
"previous" in multiple places which speaks to how difficult it is to avoid
thinking of it that way. :)
was (Author: jbellis):
bq. We point next to next, which is absolutely correct
I understand what sync is doing; my point is that xxxxSyncMarkerPosition always
points to the *last* offset before which the contents are synced, which we'll
revisit when we write another. Your own comments refer to "last" or "previous"
in multiple places which speaks to how difficult it is to avoid thinking of it
that way. :)
> 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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