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Date: Tue, 3 May 2011 17:31:16 -0500
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Subject: Re: observers in occasionally disconnected data centers
From: Ketan Gangatirkar <ketan@indeed.com>
To: user@zookeeper.apache.org
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Thanks, Mahadev.  I had seen ZOOKEEPER-892 but not ZOOKEEPER-784.  The
latter may be what we need.

I read the comments attached to that issue.  The most recent comment
was a Hudson CI message indicating that the tests against the patch
failed.  I was not able to find out more as it appears that the
configuration of the Apache Hudson has changed.  It appears that the
patch was approved but not merged into trunk, and it's now in limbo.
What is necessary to get that feature into the next release?  I may be
able to assist, depending on what's involved.  Thank you.


On Tue, May 3, 2011 at 4:17 PM, Mahadev Konar <mahadev@apache.org> wrote:
> Hi Ketan,
> =A0You 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:
>
> https://issues.apache.org/jira/browse/ZOOKEEPER-784
> and
> https://issues.apache.org/jira/browse/ZOOKEEPER-892
>
> 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
> jiras.
>
> --
> thanks
> mahadev
> @mahadevkonar
>
>
>
> On Tue, May 3, 2011 at 2:07 PM, Ketan Gangatirkar <ketan@indeed.com> wrot=
e:
>> Hi. =A0We're considering ZooKeeper for coordinating operations across
>> multiple data centers. =A0These data centers will occasionally be
>> disconnected. =A0We were planning on using observers in remote data
>> centers. =A0Our 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. =A0Is this correct? =A0Does
>> anyone have suggestions for how to work around this problem? =A0The
>> 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. =A0I imagine the disadvantages of that are obvious
>> to everyone. =A0I hope someone can share some great idea that allows me
>> to avoid that miserable fate. =A0Thanks.
>>
>> --
>> Ketan Gangatirkar
>> ketan@indeed.com
>>
>


--=20
Ketan Gangatirkar
ketan@indeed.com
Perishable Developer