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From Vishal Kher <vishalm...@gmail.com>
Subject Re: zookeeper cluster spanning datacenters
Date Thu, 22 Sep 2011 20:45:52 GMT
Hi Camille,

This is  very interesting.

Can you give more info on your setup?
- Network connectivity (bandwidth and latency) that you have between the
data centers? How much of the bandwidth is available for ZK?
- What are the timeout (server and client session timeout) values that you
use? How much latency are the applications willing to tolerate?

We are thinking of running ZK across data centers as well and it will be
great to see how others are resolving some of these problems.


On Thu, Sep 22, 2011 at 11:03 AM, Fournier, Camille F. <
Camille.Fournier@gs.com> wrote:

> We spread our ZKs across 3 data centers and in fact, these data centers are
> split across global regions (2 or 4 in one region, one in a remote region).
> To keep throughput up (and note that the throughput you have to worry about
> is only write throughput), we always ensure that the master is in one of the
> "local" data centers.
> If you have a very write-heavy and write time sensitive load, this might
> affect your performance. It won't affect reads at all because reads are
> serviced from the memory of the zk you connect to. For a mostly
> read-intensive load, splitting across data centers is unlikely to cause you
> problems.
> There is one exception: Monitoring. Even across data centers in the same
> region, we sometimes see zk dashboard unable to properly monitor the leader
> of a heavily-utilized cluster. This is due to the way the 4lw connections
> are managed, and something I'm trying to fix.
> If you have the machines to test, I would recommend running zk-smoketest  (
> https://github.com/phunt/zk-smoketest) on the proposed config.
> C
> -----Original Message-----
> From: Damu R [mailto:damu.devnull@gmail.com]
> Sent: Thursday, September 22, 2011 10:50 AM
> To: user@zookeeper.apache.org
> Subject: zookeeper cluster spanning datacenters
> Hi,
> I would like to know the downsides of having a zookeeper cluster that spans
> multiple datacenters. The requirement is a datacenter failure should not
> bring down the zookeeper cluster. From my understanding it is not possible
> to have a hot/cold cluster kind of setup possible. So we are thinking of
> putting zk servers in 3 colos(1+1+1 or 2+2+3). One of the major drawback I
> could think of is the throughput of the system affected by latency. The
> system does not require high throughput and can accept some latency. How
> much effect will the latency have on the throughput of the system? What are
> the other downsides of spreading the cluster across datacenters?
> Regards
> Damu

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