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https://issues.apache.org/jira/browse/CASSANDRA-6218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13834696#comment-13834696
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Jimmy Mårdell edited comment on CASSANDRA-6218 at 11/28/13 10:26 AM:
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I've added a patch that lets you specify which data centers should be included
in a repair. This is just a generalization of the --local flag, but now you can
specify --dc dc1,dc2 for instance.
was (Author: yarin):
Patch that makes it possible to specify which data centers should be included
in a repair.
> Reduce WAN traffic while doing repairs
> --------------------------------------
>
> Key: CASSANDRA-6218
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6218
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: sankalp kohli
> Priority: Minor
> Attachments: trunk-6218.txt
>
>
> The way we send out data that does not match over WAN can be improved.
> Example: Say there are four nodes(A,B,C,D) which are replica of a range we
> are repairing. A, B is in DC1 and C,D is in DC2. If A does not have the data
> which other replicas have, then we will have following streams
> 1) A to B and back
> 2) A to C and back(Goes over WAN)
> 3) A to D and back(Goes over WAN)
> One of the ways of doing it to reduce WAN traffic is this.
> 1) Repair A and B only with each other and C and D with each other starting
> at same time t.
> 2) Once these repairs have finished, A,B and C,D are in sync with respect to
> time t.
> 3) Now run a repair between A and C, the streams which are exchanged as a
> result of the diff will also be streamed to B and D via A and C(C and D
> behaves like a proxy to the streams).
> For a replication of DC1:2,DC2:2, the WAN traffic will get reduced by 50% and
> even more for higher replication factors.
>
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