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From Patrick Hunt <ph...@apache.org>
Subject Re: Importance of latency in a global deployment
Date Wed, 04 May 2011 18:04:18 GMT
Camille did you tune any of the server configuration parameters? I
think this would be interesting/useful for ppl.

You are correct about write latency and issues wrt a client's server
selection. This jira introduces the idea of allowing addl connection
strategies
https://issues.apache.org/jira/browse/ZOOKEEPER-781
which for this case might be interesting - the client would attempt to
connect to the "closest available server", fail over to a far server
if necessary, but then keep checking for closer servers to become
available over time (say the server recovers). Today you would fail
over to another (potentially far) server, but never reconnect back to
the closer server.

Patrick

On Wed, May 4, 2011 at 9:55 AM, Fournier, Camille F. [Tech]
<Camille.Fournier@gs.com> wrote:
> Global clusters will affect writes greatly, and may also affect you client reads in an
indirect manner.
> Writes, having to traverse from one region to another for purposes of voting, will be
slowed down considerably by the ping time between regions.
> If you did a three node deployment in the manner you mentioned, your clients may also
suffer. Usually you would want to have a list of all available cluster members for your client
to connect to, so if one is down or goes down the client can fail over to a running node.
However, given that your client will have regional affinity for at most one of your servers,
if you use the standard zk client connection logic your client either may be connected to
a far region (slowing down all responses due to latency) or the client would have no failover
node available should their close region node fail. If you choose to have clients able to
connect to any node you may also have wan traffic considerations.
>
> Some of the client side issues may be alleviated by using observers.
>
> I've got deployments across regions to handle data center failure, but in all cases the
off-region member is not available for client connections, and is kept from acting as leader
to prevent slowness on writes.
>
> C
>
> ----- Original Message -----
> From: Oliver Wulff <ownaish@gmail.com>
> To: user@zookeeper.apache.org <user@zookeeper.apache.org>
> Sent: Wed May 04 12:37:43 2011
> Subject: Importance of latency in a global deployment
>
> Hi there
>
> I'm quite new to the zookeeper project and got a question regarding
> robustness of the failover functionality in a global deployment.
>
> Are there any pre-conditions how close the zookeeper servers must be to each
> other from a geographical distance point of view?
> The reason is that the servers have to monitor and sync with each other in
> realtime and the latency might play an important role if for instance one
> server is in the US, one in Europe and one in China.
>
> Thanks
> Oli
>

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