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From Eric tamme <eta...@gmail.com>
Subject Re: Replica data distributing between racks
Date Wed, 04 May 2011 15:05:52 GMT
On Wed, May 4, 2011 at 10:09 AM, Konstantin  Naryshkin
<konstantinn@a-bb.net> wrote:
> The way that I understand it (and that seems to be consistent with what was said in this
discussion) is that each DC has its own data space. Using your simplified 1-10 system:
>   DC1   DC2
> 0  D1R1  D2R2
> 1  D1R1  D2R1
> 2  D1R1  D2R1
> 3  D1R1  D2R1
> 4  D1R1  D2R1
> 5  D1R2  D2R1
> 6  D1R2  D2R2
> 7  D1R2  D2R2
> 8  D1R2  D2R2
> 9  D1R2  D2R2
>
> Each node is responsible for half of the ring in its own DC.

Okay that makes sense from a primary distribution perspective, but how
do the nodes magically know where to send the data?  When using NTS,
if there are two nodes that overlap tokens, does NTS choose the
"closest" node to place the primary on?  If that is the case, then it
makes sense.

As far as the replication distribution... with a replica going to each
data center {DC1:1,DC2:1} does NTS take the token and find the
"closest" node in the opposite data center? ... so for token 7 in D1
replicating to D2, it will look for a node with a token range closest
to that? In this scenario it would go to D2R2?

That makes sense as far as why the replication was hot spotting before
where my tokens were N,M,O,P  where N<M<O<P  any replica for N or M
would get pinned to O, and any replicate for O or P would get pinned
to M.

I think the biggest confusion for me here was that .. I did not know
you could have overlapping key ranges.  Can you only do this when
using NTS?  I was stuck in the mind set of a "single ring" of tokens.

Thanks again
-Eric

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