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From Botond Hejj <Botond.H...@MorganStanley.com>
Subject Re: leader election length
Date Tue, 13 Dec 2011 10:55:40 GMT
Thanks Camille,

Sorry, my assumption was wrong. I've made now a test and indeed the
session doesn't expire in this case.
This means than the only problem is that the service is down for an
increasing amount of time if snapshot is increasing. We use SAN to
store the snapshot and reading it back twice during leader election
can be a little slow (~30 secs). It is not bad at all but still have
anybody tried making the leader election faster in this case?

Regards,
Botond

On Mon, Dec 12, 2011 at 18:35, Camille Fournier <camille@apache.org> wrote:
> Existing sessions will not expire from the server side during election.
> Your client code may choose to close them on its end if you sit in a
> DISCONNECTED state for too long, but nothing should be expiring the
> sessions while quorum is not available.
>
> C
>
> On Mon, Dec 12, 2011 at 12:06 PM, Botond Hejj <Botond.Hejj@morganstanley.com
>> wrote:
>
>> Hi ZooKeeper users,
>>
>> I am playing currently with zookeeper and testing what happens if the
>> leader of an ensemble goes down.
>> I know that during the leader election zookeeper server won't reply to
>> any requests and if leader election takes a long time than existing
>> sessions might expire.
>> What I see in my tests that each server reads the last snapshot file
>> to get last zxid for leader election and when the leader is elected
>> than the leader reads the snapshot again before it syncs the
>> followers.
>>
>> This means that the more data we store in zookeeper the longer it
>> takes to elect a new leader. This is also means as load of the
>> ensemble increases clients need bigger session timeout to "survive"
>> the loss of the leader.
>>
>> Is it possible to do anything about this and have a fast leader
>> election even if the snapshot is big?
>>
>> Regards,
>> Botond Hejj
>>



-- 
Botond Hejj
Morgan Stanley | Technology
Lechner Odon fasor 8 | Floor 07
Budapest, 1095
Phone: +36 1 881-3962
Botond.Hejj@MorganStanley.com

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