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From Nomar Morado <j316servi...@icloud.com>
Subject Re: observer changing to participant when there is no quorum
Date Wed, 15 Jun 2016 13:33:22 GMT
Corrected typos

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> On Jun 15, 2016, at 9:31 AM, Nomar Morado <j316services@icloud.com> wrote:
> 
> This is what I have done so far:
> 
> A,B,C are participants
> C,D are observers
> 
> B,C are offline (crashed)
> 
> I am trying to:
> 
> 1. Remove C, D
> 2. Add C,D back as participants
> 
> Will this work?
> 
> At least in my testing (might be doing wrong) I am getting this error on the first step
and hence can't get forward:
> 
> Client could not connect to reestablished  quorum: giving up after 30+ seconds
> 
> 
> I am passing the original server configure string to zk's reconfig method.
> 
> 
> 
> Thanks
> 
> 
> Printing e-mails wastes valuable natural resources. Please don't print this message
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> 
> Sent from my iPhone
> 
>> On Jun 14, 2016, at 10:55 PM, Alexander Shraer <shralex@gmail.com> wrote:
>> 
>> Right, a quorum of participants from the old config is required to process
>> any command, including reconfig,
>> and a quorum of participants from the new config is required for the
>> reconfig to even start. If there's no such connected
>> quorum an error NewConfigNoQuorum will be thrown.
>> 
>> But there is one slightly confusing case where the error is thrown, which
>> is explained in the doc: when you are
>> converting an observer to a participant and there is no quorum in the new
>> config without counting that "future" participant.
>> So the server is connected, but since its not a participant we get the
>> error above.  In that case, one first needs to
>> convert the observer to remove the observer and then add it back. The
>> detailed explanation is in the doc, look for
>> "Changing an observer into a follower".
>> 
>> On Wed, Jun 15, 2016 at 1:17 AM, Camille Fournier <camille@apache.org>
>> wrote:
>> 
>>> I'm finding the documentation quite confusing. I was under the impression
>>> that quorum of some sort was needed to do a reconfig. Can you reconfig when
>>> there is no quorum?
>>> 
>>> *Progress guarantees:* Up to the invocation of the reconfig operation, a
>>> quorum of the old configuration is required to be available and connected
>>> for ZooKeeper to be able to make progress. Once reconfig is invoked, a
>>> quorum of both the old and of the new configurations must be available.
>>> 
>>> *Adding servers:* Before a reconfiguration is invoked, the administrator
>>> must make sure that a quorum (majority) of participants from the new
>>> configuration are already connected and synced with the current leader.
>>> 
>>> 
>>> 
>>> On Tue, Jun 14, 2016 at 5:35 PM, Alexander Shraer <shralex@gmail.com>
>>> wrote:
>>> 
>>>> This is needed only in case the target config doesn't have a quorum which
>>>> are already followers in the old config
>>>> and are up. We need agreement from a quorum of the target config, but
>>>> observers aren't participating
>>>> in the voting protocol.
>>>> 
>>>>> On Tue, Jun 14, 2016 at 7:35 PM, Michael Han <hanm@cloudera.com>
wrote:
>>>>> 
>>>>> This might help:
>>>>> https://zookeeper.apache.org/doc/trunk/zookeeperReconfig.html section
>>>>> '*Changing
>>>>> an observer into a follower:'*
>>>>> "first invoke a reconfig to remove D from the configuration and then
>>>> invoke
>>>>> a second command to add it back as a participant (follower)."
>>>>> 
>>>>> 
>>>>> On Tue, Jun 14, 2016 at 8:53 AM, Nomar Morado <nomar.morado@gmail.com>
>>>>> wrote:
>>>>> 
>>>>>> Hi
>>>>>> 
>>>>>> I was trying to promote an observer into participant when ZK loses
>>>>> quorum -
>>>>>> but it seems that it does not allow to.
>>>>>> 
>>>>>> Would you know how this can be accomplished without having to recycle
>>>> ZK?
>>>>>> 
>>>>>> I am using 3.5.0-alpha
>>>>>> 
>>>>>> 
>>>>>> Thanks.
>>>>> 
>>>>> 
>>>>> 
>>>>> --
>>>>> Cheers
>>>>> Michael.
>>> 

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