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From "Flavio Junqueira" <fpjunque...@yahoo.com>
Subject RE: ZOOKEEPER-900 / 901 / 1678
Date Wed, 30 Apr 2014 22:04:31 GMT
Leader election seems to be taking a long time. The connection attempts from QuorumCnxManager
are not causing a new round of leader election. What causes it is the absence of a quorum
of supporters, so the elected leader is not getting enough servers to support it.

-Flavio

-----Original Message-----
From: Cameron McKenzie [mailto:mckenzie.cam@gmail.com] 
Sent: Wednesday, April 30, 2014 10:36 PM
To: user@zookeeper.apache.org
Subject: Re: ZOOKEEPER-900 / 901 / 1678

I've done a bit more testing this morning, and it appears that the leader election is actually
completing, but then just after the election has completed, the connection attempt to the
dead host times out, and this seems to cause another leader election. The same thing happens
the next leader election. etc.

2014-04-30 04:07:25,383 [myid:3] - INFO
[QuorumPeer[myid=3]/0:0:0:0:0:0:0:0:2183:Leader@358] - LEADING - LEADER ELECTION TOOK - 14662
2014-04-30 04:07:25,756 [myid:3] - WARN
[WorkerSender[myid=3]:QuorumCnxManager@382] - Cannot open channel to 2 at election address
/10.0.0.0:3889
java.net.SocketTimeoutException: connect timed out
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at
java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
        at
java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
        at
java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
        at java.net.Socket.connect(Socket.java:579)
        at
org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:368)
        at
org.apache.zookeeper.server.quorum.QuorumCnxManager.toSend(QuorumCnxManager.java:341)
        at
org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.process(FastLeaderElection.java:449)
        at
org.apache.zookeeper.server.quorum.FastLeaderElection$Messenger$WorkerSender.run(FastLeaderElection.java:430)
        at java.lang.Thread.run(Thread.java:744)
2014-04-30 04:07:25,757 [myid:3] - INFO
[WorkerReceiver[myid=3]:FastLeaderElection@597] - Notification: 1 (message format version),
3 (n.leader), 0xc00000001 (n.zxid), 0xb (n.round), LOOKING (n.state), 3 (n.sid), 0xd (n.peerEpoch)
LEADING (my state)

cheers



On Wed, Apr 30, 2014 at 6:48 PM, Cameron McKenzie <mckenzie.cam@gmail.com>wrote:

> hey Flavio,
> Thanks for the quick reply.
>
> I'm running ZK 3.4.6. Having looked into the code a bit more, I think 
> that I was slightly presumptuous about the root cause. The actual 
> socket connects seem to be passing a timeout correctly, and based on 
> the logs, I can see the timeouts on connect occurring.
>
> I can reproduce the issue on a VM running two instances of ZK. These 
> instances are configured in a 3 node cluster (with the 2 real ZK 
> instances, and one bogus IP address that will not resolve to anything useful).
> Specifically, this bogus host is configured 2nd in the server list. 
> When I configured it third, the cluster would occasionally form a 
> quorum (though still not consistently). I've attached the config and 
> logs from both of the ZK instances.
>
> Any help would be much appreciated!
> cheers
>
>
>
>
> On Wed, Apr 30, 2014 at 6:09 PM, FPJ <fpjunqueira@yahoo.com> wrote:
>
>> Hi Cameron,
>>
>> Which version of ZK are you using? Also, if you can share logs, then 
>> it might be easier for us to help you out.
>>
>> -Flavio
>>
>> > -----Original Message-----
>> > From: Cameron McKenzie [mailto:mckenzie.cam@gmail.com]
>> > Sent: 30 April 2014 08:44
>> > To: zookeeper-user@hadoop.apache.org
>> > Subject: ZOOKEEPER-900 / 901 / 1678
>> >
>> > ZooKeeper users,
>> > Does anyone know the status of these issues? They don't seem to 
>> > have had anything done to them since late 2010?
>> >
>> > I think that we're experiencing the same issue currently. If we 
>> > have a
>> 3 node
>> > cluster for example, and 1 of these nodes is completely dead (i.e 
>> > the
>> entire
>> > host is not contactable due to a power outage), I would expect that 
>> > a quorum could still be formed, but this does not appear to be the case.
>> >
>> > I haven't delved into the code too much, but it appears that 
>> > blocking
>> IO is
>> > being used for the connect. This doesn't respect the socket SO 
>> > timeout
>> being
>> > set, so it means that the connect() call can block for some 
>> > arbitrary
>> amount of
>> > time (based on the OS level TCP settings?). This in turn means that
>> leader
>> > election will fail because it times out before the socket connect 
>> > does,
>> even
>> > though there are enough live hosts present to form a quorum.
>> >
>> > This seems like a fairly fundamental problem, unless I'm missing
>> something.
>> > If a single host goes down due to a power failure for example, it 
>> > can
>> prevent
>> > any further hosts joining the cluster. In addition, if after a 
>> > power
>> failure,
>> > enough hosts come back online to form a quorum, but some don't, 
>> > that a quorum may still not be able to be formed.
>> > cheers
>> > Cam
>>
>>
>


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