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From "Yuki Morishita (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8193) Multi-DC parallel snapshot repair
Date Wed, 12 Nov 2014 00:05:34 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14207377#comment-14207377
] 

Yuki Morishita commented on CASSANDRA-8193:
-------------------------------------------

First of all, thanks for the patch!
I review it based on 2.0, but because the patch adds new feature, I'd rather put this to 2.1+.
(So go ahead and apply 2.0.x yourself after review).

So, some comments:

* If replication factor is set to be 1 for each DC, then it will be the same as ParallelRequestCoordinator.
There needs fall back to current behavior in this case.
* It looks like ParallelRequestCoordinator class can be {{... implements IRequestCoordinator<InetAddress>}}.
* DatacenterAwareRequestCoordinator uses AtomicInteger, but primitive int just works here.
* nit: put braces on a new line.

> Multi-DC parallel snapshot repair
> ---------------------------------
>
>                 Key: CASSANDRA-8193
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8193
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jimmy MÃ¥rdell
>            Assignee: Jimmy MÃ¥rdell
>            Priority: Minor
>             Fix For: 2.0.12
>
>         Attachments: cassandra-2.0-8193-1.txt
>
>
> The current behaviour of snapshot repair is to let one node at a time calculate a merkle
tree. This is to ensure only one node at a time is doing the expensive calculation. The drawback
is that it takes even longer time to do the merkle tree calculation.
> In a multi-DC setup, I think it would make more sense to have one node in each DC calculate
the merkle tree at the same time. This would yield a significant improvement when you have
many data centers.
> I'm not sure how relevant this is in 2.1, but I don't see us upgrading to 2.1 any time
soon. Unless there is an obvious drawback that I'm missing, I'd like to implement this in
the 2.0 branch.



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