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https://issues.apache.org/jira/browse/CASSANDRA-4189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13262066#comment-13262066
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Jonathan Ellis commented on CASSANDRA-4189:
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bq. 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.

Not sure this is a problem now that we drop the tombstones after each handoff.  
Since there is only one handoff per target at a time, we don't need to worry 
about having to skip tombstones in a meaningful volume.

bq. What i am suggesting is to throttle but in a multi threaded way

+1
                
> 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
>
>
> 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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