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From "Mullen, Robert" <>
Subject Re: Clarification on how multi-DC replication works
Date Tue, 11 Feb 2014 16:16:18 GMT
I had the same question a while back and put together this picture to help
me understand the flow of data for multi region deployments. Hope that it

On Mon, Feb 10, 2014 at 7:52 PM, Sameer Farooqui <>wrote:

> Hi,
> I was hoping someone could clarify a point about multi-DC replication.
> Let's say I have 2 data centers configured with replication factor = 3 in
> each DC.
> My client app is sitting in DC 1 and is able to intelligently pick a
> coordinator that will also be a replica partner.
> So the client app sends a write with consistency for DC1 = Q and
> consistency for DC2 = Q to a coordinator node in DC1.
> That coordinator in DC1 forwards the write to 2 other nodes in DC1 and a
> coordinator in DC2.
> Is it correct that all 3 nodes in DC2 will respond back to the original
> coordinator in DC1? Or will the DC2 nodes respond back to the DC2
> coordinator?
> Let's say one of the replica nodes in DC2 is down. Who will hold the hint
> for that node? The original coordinator in DC1 or the coordinator in DC2?

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