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From aaron morton <aa...@thelastpickle.com>
Subject Re: Inter-DC communication optimization
Date Mon, 29 Apr 2013 20:07:06 GMT
Messages are sent to all replicas involved in there request at the same time. All nodes in
the cluster must be able to communicate to all other nodes.

The coordinator the client is talking to, the local coordinator, groups messages (for one
read/mutation) to be sent to remove data centres and only sends a single message to one node
in each remote DC. In each remote DC the receiving node then acts as a remote coordinator
which forwards the messages to the other replicas. All replicas in any DC (local and remotes)
reply directly back to the local DC. 

Cheers

-----------------
Aaron Morton
Freelance Cassandra Consultant
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 29/04/2013, at 11:47 PM, Sergey Naumov <sknaumov@gmail.com> wrote:

> Hello.
> 
> I would like to know whether updates are propagated from local DC to remote DCs simultaneously
(so All-to-All network connections are preferable) or Cassandra can somehow determine nearest
DCs and send updates only to them (so these nearest DCs have to propagate updates further)?
> Is there some optimizations for multiple DCs placed sequentially on a single link like
DC1 <-> DC2 <-> ... <-> DCn?
> 
> Thanks in advance,
> Sergey Naumov.


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