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From Andor Molnar <an...@cloudera.com.INVALID>
Subject Re: Leader election failing
Date Wed, 08 Aug 2018 15:05:28 GMT
Some kind of a network split?

It looks like 1-2 and 3-4 were able to communicate each other, but
connection timed out between these 2 splits. When 5 came back online it
started with supporters of (1,2) and later 3 and 4 also joined.

There was no such issue the day after.

Which version of ZooKeeper is this? 3.5.something?


On Wed, Aug 8, 2018 at 4:52 PM, Chris <c.turksema@gmail.com> wrote:

> Actually i have similar issues on my test and acceptance clusters where
> leader election fails if the cluster has been running for a couple of days.
> If you stop/start the Zookeepers once they will work fine on further
> disruptions that day. Not sure yet what the treshold is.
> On 8 August 2018 4:32:56 pm Camille Fournier <camille@apache.org> wrote:
> Hard to say. It looks like about 15 minutes after your first incident where
>> 5 goes down and then comes back up, servers 1 and 2 get socket errors to
>> their connections with 3, 4, and 6. It's possible if you had waited those
>> 15 minutes, once those errors cleared the quorum would've formed with the
>> other servers. But as for why there were those errors in the first place
>> it's not clear. Could be a network glitch, or an obscure bug in the
>> connection logic. Has anyone else ever seen this?
>> If you see it again, getting a stack trace of the servers when they can't
>> form quorum might be helpful.
>> On Wed, Aug 8, 2018 at 11:52 AM Cee Tee <c.turksema@gmail.com> wrote:
>> I have a cluster of 5 participants (id 1-5) and 1 observer (id 6).
>>> 1,2,5 are in datacenter A. 3,4,6 are in datacenter B.
>>> Yesterday one of the participants (id5, by chance was the leader) was
>>> rebooted. Although all other servers were online and not suffering from
>>> networking issues the leader election failed and the cluster remained
>>> "looking" until the old leader came back online after which it was
>>> promptly
>>> elected as leader again.
>>> Today we tried the same exercise on the exact same servers, 5 was still
>>> leader and was rebooted, and leader election worked fine with 4 as new
>>> leader.
>>> I have included the logs.  From the logs i see that yesterday 1,2 never
>>> received new leader proposals from 3,4 and vice versa.
>>> Today all proposals came through. This is not the first time we've seen
>>> this type of behavior, where some zookeepers can't seem to find each
>>> other
>>> after the leader goes down.
>>> All servers use dynamic configuration and have the same config node.
>>> How could this be explained? These servers also host a replicated
>>> database
>>> cluster and have no history of db replication issues.
>>> Thanks,
>>> Chris

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