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From Patrick Hunt <ph...@apache.org>
Subject Re: observers in occasionally disconnected data centers
Date Tue, 03 May 2011 22:46:26 GMT
The core tests failed on last hudson, I just kicked off a patch build,
seems recent changes (logging?) have caused the patch to stop

Ketan would you like to try updating the patch and resubmit?


On Tue, May 3, 2011 at 3:31 PM, Ketan Gangatirkar <ketan@indeed.com> wrote:
> 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,
>>  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:
>> 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> 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
> --
> Ketan Gangatirkar
> ketan@indeed.com
> Perishable Developer

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