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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1530) More-efficient cross-DC replication
Date Tue, 30 Nov 2010 21:34:14 GMT


Jonathan Ellis commented on CASSANDRA-1530:

I don't think so; the extra hop is by definition in the same DC as the destination, so it
should be negligible compared to cross-DC latency unless something is going wrong (and something
going wrong is why we have the timeout to protect us, so increasing it in that situation doesn't
make sense).

> More-efficient cross-DC replication
> -----------------------------------
>                 Key: CASSANDRA-1530
>                 URL:
>             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
> 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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