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From Ketan Gangatirkar <ke...@indeed.com>
Subject Re: observers in occasionally disconnected data centers
Date Wed, 04 May 2011 16:57:42 GMT
Got the patch formatted right and applying successfully, now I'll see
if I can figure out the unit test failure.

On Wed, May 4, 2011 at 11:26 AM, Patrick Hunt <phunt@apache.org> wrote:
> Hi Ketan, the patch is failing to apply
> https://builds.apache.org/hudson/job/PreCommit-ZOOKEEPER-Build/246//console
>
> Looks like you used git, I usually do something like:
> git diff rev1..rev2 --no-prefix > ZOOKEEPER-784.patch
> can you give it another try?
>
> Patrick
>
> On Tue, May 3, 2011 at 6:42 PM, Ketan Gangatirkar <ketan@indeed.com> wrote:
>> I have updated Sergey's patch to:
>>
>> * apply to current trunk
>> * incorporate one trivial output change he made to StatCommand in
>> NettyServerCnxn.java
>> * change log4j references to slf4j
>>
>> I have successfully run ant releaseaudit on the result.  The updated
>> patch is now attached to the issue:
>>
>> https://issues.apache.org/jira/browse/ZOOKEEPER-784
>>
>> I do *not* make any claim to have understood the contents of this
>> patch; all I did was synch everything and fix the obvious log4j/slf4j
>> change.  Now what?
>>
>>
>> On Tue, May 3, 2011 at 5:46 PM, Patrick Hunt <phunt@apache.org> wrote:
>>> The core tests failed on last hudson, I just kicked off a patch build,
>>> seems recent changes (logging?) have caused the patch to stop
>>> applying:
>>> https://hudson.apache.org/hudson/view/S-Z/view/ZooKeeper/job/PreCommit-ZOOKEEPER-Build/238/console
>>>
>>> Ketan would you like to try updating the patch and resubmit?
>>>
>>> Patrick
>>>
>>> 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
>>>>
>>>
>>
>>
>>
>> --
>> Ketan Gangatirkar
>> ketan@indeed.com
>> Perishable Developer
>>
>



-- 
Ketan Gangatirkar
ketan@indeed.com
Perishable Developer

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