[jira] [Comment Edited] (CASSANDRA-6218) Reduce WAN traffic while doing repairs

["Jimmy Mårdell (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-6218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13834696#comment-13834696 ] 

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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