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Date: Thu, 9 Dec 2010 16:37:04 -0500 (EST)
From: "T Jake Luciani (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Subject: [jira] Commented: (CASSANDRA-1530) More-efficient cross-DC
 replication
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    [ https://issues.apache.org/jira/browse/CASSANDRA-1530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12969956#action_12969956 ] 

T Jake Luciani commented on CASSANDRA-1530:
-------------------------------------------


bq. one thing I don't like still is how groupEndpointsByDataCenter does some grouping but also some insertLocalMessages. not a clean separation of functionality.

Yeah, I couldn't think of a way to avoid this without doing two passes.  I think leaving it as it was ( one huge block of code)  is worse though.

Otherwise your patch seems fine. 

> More-efficient cross-DC replication
> -----------------------------------
>
>                 Key: CASSANDRA-1530
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1530
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: T Jake Luciani
>             Fix For: 0.7.1
>
>         Attachments: 1530-cleaned.txt, 1530-joaquin.txt, 1530-v5.txt, 1530_v2.txt
>
>
> Currently the coordinator node sends writes to each replica.  In multi-dc situations, it would be more efficient to have the coordinator talk to a single node in each DC, which would forward the writes to the other replicas local to it.  (All replicas would continue to ack to the coordinator.)
> Shouldn't be difficult to add a header to RMVH saying "consult the Strategy to see who else is local to you and queue it off to them as well."
> For example, consider two data centers with the following nodes:
> DC1: A, B, C
> DC2: D, E, F
> A client connected to node A performs an insert that should be replicated to {B,C,E,F}.  Currently, A will send a MUTATION verb to each of those nodes directly.  But communication to E and F is relatively expensive since they are in the other data center from A.  So we'd like to send the mutation to just one, say E, with a tag saying "forward this to F as well."

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