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From Anand Parthasarathy <anpar...@avinetworks.com>
Subject Re: Zookeeper leader election takes a long time.
Date Mon, 10 Oct 2016 17:15:38 GMT
Folks,

Any insight into this or any workarounds that you can think of to mitigate
against this issue? We have isolated it to a test setup, where we are able
to reproduce this somewhat consistently if we keep a node powered off.

Thanks,
Anand.

On Sat, Oct 8, 2016 at 10:05 AM, Anand Parthasarathy <
anpartha@avinetworks.com> wrote:

> Hi Flavio,
>
> I have attached the logs from node 1 and node 3. Node 2 was powered off
> around 10-03 12:36. Leader election kept going until 10-03 15:57:16 when it
> finally converged.
>
> Thanks,
> Anand.
>
> On Sat, Oct 8, 2016 at 7:55 AM, Flavio Junqueira <fpj@apache.org> wrote:
>
>> Hi Anand,
>>
>> I don't understand whether 1 and 3 were able or even trying to connect to
>> each other. They should be able to elect a leader between them and make
>> progress. You might want to upload logs and let us know.
>>
>> -Flavio
>>
>> > On 08 Oct 2016, at 02:11, Anand Parthasarathy <anpartha@avinetworks.com>
>> wrote:
>> >
>> > Hi,
>> >
>> > We are currently using zookeeper 3.4.6 version and use a 3 node
>> solution in
>> > our system. We see that occasionally, when a node is powered off (in
>> this
>> > instance, it was actually a leader node), the remaining two nodes do not
>> > form a quorum for a really long time. Looking at the logs, it appears
>> the
>> > sequence is as follows:
>> > - Node 2 is the zookeeper leader
>> > - Node 2 is powered off
>> > - Node 1 and Node 3 recognize and start the election
>> > - Node 3 times out after initLimit * tickTime with "Timeout while
>> waiting
>> > for quorum" for Round N
>> > - Node 1 times out after initLimit * tickTime with "Exception while
>> trying
>> > to follow leader" for Round N+1 at the same time.
>> > - And the process continues where N is sequentially incrementing.
>> > - This happens for a long time.
>> > - In one instance, we used tickTime=5000 and initLimit=20 and it took
>> > around 3.5 hours to converge.
>> > - In a given round, Node 1 will try connecting to Node 2, gets
>> connection
>> > refused waits for notification timeout which increases by 2 every
>> iteration
>> > until it hits the initLimit. Connection Refused is because the node 2
>> comes
>> > up after reboot, but zookeeper process is not started (due to a
>> different
>> > failure).
>> >
>> > It looks similar to ZOOKEEPER-2164 but there it is a connection timeout
>> > where Node 2 is not reachable.
>> >
>> > Could you pls. share if you have seen this issue and if so, what is the
>> > workaround that can be employed in 3.4.6.
>> >
>> > Thanks,
>> > Anand.
>>
>>
>

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