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From Mahadev Konar <maha...@apache.org>
Subject Re: observers in occasionally disconnected data centers
Date Tue, 03 May 2011 21:17:50 GMT
Hi Ketan,
 You are correct that observers need connection to quorum as well.
There have been quite a few discussions on multi colo replication and
read only mode of ZooKeeper.

Here are the jiras for those:


These have been mostly targeted at exactly a use case like yours.
Please take a look and them and feel free to contribute/comment on the


On Tue, May 3, 2011 at 2:07 PM, Ketan Gangatirkar <ketan@indeed.com> wrote:
> Hi.  We're considering ZooKeeper for coordinating operations across
> multiple data centers.  These data centers will occasionally be
> disconnected.  We were planning on using observers in remote data
> centers.  Our applications can survive being unable to *write* to
> ZooKeeper, but they do need to be able to read from it, even if the
> data were stale.
> On further examination, it looks like observers must always be
> connected to the quorum to function at all.  Is this correct?  Does
> anyone have suggestions for how to work around this problem?  The
> first thing that comes to mind is duplicating the required data in
> some other local data store and falling back on that when the DC
> becomes disconnected.  I imagine the disadvantages of that are obvious
> to everyone.  I hope someone can share some great idea that allows me
> to avoid that miserable fate.  Thanks.
> --
> Ketan Gangatirkar
> ketan@indeed.com

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