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From Sasha Dolgy <sdo...@gmail.com>
Subject Re: Location-aware replication based on objects' access pattern
Date Wed, 06 Apr 2011 07:55:29 GMT
I had been asked this question from a strategy point of view, and
referenced how linkedin.com appears to handle this.

<assumption>
Specific region data is stored on a ring in that region.  While based
in the middle east, my linkedin.com profile was kept on the middle
east part of linkedin.com ... when I moved back to europe, updated my
city, my profile shifted from the middle east to europe ...
</assumption>

would it not be easier to manage multiple rings (one in each required
geographic region) to suit the location aware use case?  This way you
can grow out that region as necessary and invest less into the regions
that aren't as busy ...

would mean your application needs to be aware of the different regions
and where data exists ... or make some initial assumptions as to where
to find data ...

- 1 ring for apac
- 1 ring for europe
- 1 ring for americas
- 1 global ring (with nodes present in each region)

the global ring maintains reference data on which ring a guid exists ...

I've been playing with this concept on AWS ... the amount of data I
have isn't significant, so I may not have run into problems that will
occur when i get to large amounts of data ...

-sd

On Wed, Apr 6, 2011 at 9:26 AM, Jonathan Colby <jonathan.colby@gmail.com> wrote:
> good to see a discussion on this.
>
> This also has practical use for business continuity where you can control that the clients
in a given data center first write replicas to its own data center, then to the other data
center for backup.  If I understand correctly, a write takes the token into account first,
then the replication strategy decides where the replicas go.   I would like to see the the
first writes to be based on "location" instead of token -   whether that is accomplished
by manipulating the key or some other mechanism.
>
> That way, if you do suffer the loss of a data center,  the clients are guaranteed to
meet quorum on the nodes in its own data center  (given  a mirrored architecture across
2 data centers).
>
> We have 2 data centers.  If one goes down we have the problem that quorum cannot be
satisfied for half of the reads.

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