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From Anand Parthasarathy <anpar...@avinetworks.com>
Subject Re: Zookeeper leader election takes a long time.
Date Tue, 11 Oct 2016 21:56:46 GMT
Folks,

Sending a quick note again to find out if there is any insight the
community can offer in terms of a solution or workaround? We use zookeeper
for service discovery in our product and this issue has surfaced in a large
customer site a couple of times and we need to figure out a solution soon.

Thanks,
Anand.

On Mon, Oct 10, 2016 at 10:15 AM, Anand Parthasarathy <
anpartha@avinetworks.com> wrote:

> 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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