[jira] [Commented] (CASSANDRA-4189) Improve hints replay

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-4189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13292370#comment-13292370 ] 

Jonathan Ellis commented on CASSANDRA-4189:
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I don't see a ton of benefit from multiple threads trying to run deliverHintsToEndpointInternal to the same target, and a lot of contention/duplicate handoff attempts (hence, CASSANDRA-4320).

Restricting the handoff workers to different targets would be a straightforward improvement (sounds like this would still address your use case above).
                
> Improve hints replay
> --------------------
>
>                 Key: CASSANDRA-4189
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4189
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 1.2
>            Reporter: Vijay
>            Assignee: Vijay
>            Priority: Minor
>             Fix For: 1.2
>
>         Attachments: 0001-CASSANDRA-4189.patch
>
>
> Problem: Hints are stored in one row.
> when there are a lot of hints stored and we store Tombstones for the ones which has been replayed.
> It might be worth shading the hints based on Hour at which the hints are stored. This can reduce the complexity of the scanning for hints.
> Problem: Hints replay is too slow and single threaded.
> There are use-case where the hints needs to be replayed ASAP to make the cluster more consistent.
> In Multi region cluster, the throttle is already done due to the latency which is in the order of 100's of millisecond.
> It might be worth trying to replay the hints in parallel and throttle on the number of bytes read from the disk or use the existing setting of throttle based on sleep interval on all the threads.

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