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From Ketan Gangatirkar <ke...@indeed.com>
Subject Re: observers in occasionally disconnected data centers
Date Fri, 06 May 2011 11:33:35 GMT
Hi, Patrick.  Were you able to get any assistance from the hudson
admins?  Thanks.

On Wed, May 4, 2011 at 12:53 PM, Patrick Hunt <phunt@apache.org> wrote:
> This is odd, it's failing in the c tests but for a weird reason:
>
> in:
> https://builds.apache.org/hudson/job/PreCommit-ZOOKEEPER-Build/247/artifact/trunk/build/tmp/zk.log
>
> it says:
> /grid/0/hudson/hudson-slave/workspace/PreCommit-ZOOKEEPER-Build/trunk/src/c/tests/zkServer.sh:
> line 115: java: command not found
>
> I'll ping the hudson admins and see if this is a known issue (also
> hudson is very slow today for some reason).
>
> Once that's addressed we should be good to go.
>
> Patrick
>
> On Wed, May 4, 2011 at 9:57 AM, Ketan Gangatirkar <ketan@indeed.com> wrote:
>> 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
>>
>



-- 
Ketan Gangatirkar
ketan@indeed.com
Perishable Developer

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