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Zookeeper, mail # user - Does Leader Election Have a "Settling" period?


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Mark Gius 2012-05-10, 20:35
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Flavio Junqueira 2012-05-11, 11:25
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Re: Does Leader Election Have a "Settling" period?
Mark Gius 2012-05-11, 17:08
Hmm... so then it looks like the problem was that I needed to give 3 a
little more time to join the quorum before shooting 1 so as to maintain
quorum throughout the test.  I'll give that a shot.   Thanks!

Mark

On Fri, May 11, 2012 at 4:25 AM, Flavio Junqueira <[EMAIL PROTECTED]> wrote:

> Hi Mark, From your logs, server 2 was leading and was followed only by
> server 1:
>
> 2012-05-09 01:07:25,523 - INFO
>  [QuorumPeer:/0:0:0:0:0:0:0:0:2183:Leader@390] - Shutdown called
> java.lang.Exception: shutdown Leader! reason: Only 0 followers, need 1
>        at
> org.apache.zookeeper.server.quorum.Leader.shutdown(Leader.java:390)
>        at org.apache.zookeeper.server.quorum.Leader.lead(Leader.java:367)
>        at
> org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:658)
>
> Consequently when you shut down 1 the ensemble lost quorum. The sequence
> of notifications made 3 think that it was leading, but it didn't become
> established as a leader because it didn't have a quorum supporting.
> Eventually 3 gives up and starts following 2:
>
> 2012-05-09 01:08:08,961 - INFO  [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 2 (n.leader), 4294967297
> (n.zxid), 2 (n.round), LOOKING (n.state), 3 (n.sid), LOOKING (my state)
> 2012-05-09 01:08:09,163 - INFO
>  [QuorumPeer:/0:0:0:0:0:0:0:0:2184:QuorumPeer@643] - FOLLOWING
>
> and 2 leading:
>
> 2012-05-09 01:08:08,959 - INFO  [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 2 (n.leader), 4294967297
> (n.zxid), 2 (n.round), LOOKING (n.state), 2 (n.sid), LOOKING (my state)
> 2012-05-09 01:08:08,959 - INFO  [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 3 (n.leader), 0 (n.zxid),
> 2 (n.round), LOOKING (n.state), 3 (n.sid), LOOKING (my state)
> 2012-05-09 01:08:08,961 - INFO  [WorkerReceiver
> Thread:FastLeaderElection@496] - Notification: 2 (n.leader), 4294967297
> (n.zxid), 2 (n.round), LOOKING (n.state), 3 (n.sid), LOOKING (my state)
> 2012-05-09 01:08:09,162 - INFO
>  [QuorumPeer:/0:0:0:0:0:0:0:0:2183:QuorumPeer@655] - LEADING
>
> I'm not sure why it took so much time for the notifications to propagate,
> though.
>
> -Flavio
>
> On May 10, 2012, at 10:35 PM, Mark Gius wrote:
>
> > I'm doing some testing around a Client being connected to a zookeeper
> > endpoint that goes away and I'm seeing what appears to be a "settling"
> > period that is causing some errors.
> >
> > The test is as follows:
> >
> > 1) Three zookeeper servers are started up on the same host, configured to
> > cluster with each other.
> > 2) A Client is created and attaches to Server 1 (using
> > deterministic_conn_order flag to force this)
> > 3) Shut down Server 1 (which is NOT the Leader)
> > 4) Servers 2 and 3 still have quorum.  Interruption of service should be
> > minimal.
> > 5) The Client _should_ reconnect immediately to Server 2 or 3.
> >
> > The behavior I am seeing in practice is that after shutting down Server 1
> > quorum is lost and the Client takes on the order of 15-20 seconds to
> > re-establish a connection to the cluster.  I do not see this behavior on
> a
> > cluster that has existed for some time (say, 30-60 seconds).  I also do
> not
> > see this problem on a cluster whose tickTime has been decreased to 100ms
> > from the default of 2000ms.
> >
> > Is there a settling period that occurs immediately after a Leader is
> > elected such that quorate changes during that time cause a full leader
> > election when one might not otherwise be necessary?  If so, where can I
> > find information about how this settling period behaves?
> >
> > I have uploaded the logs for each of the three zookeeper servers here:
> > https://gist.github.com/2655709
> >
> > Mark
>
>
>
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Martin Kou 2012-05-10, 23:45