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From "FPJ" <fpjunque...@yahoo.com>
Subject RE: Disqualify a node from leader election
Date Mon, 25 Nov 2013 16:12:23 GMT
The problem with this solution is that setting the weight of E to zero will
make its acknowledgments not count for committing txns or anything in the
system that requires a quorum. Also, I don't think it prevents E from being
elected, E is still eligible because it is a participant (but with vote
zero).

-Flavio

> -----Original Message-----
> From: Kuba Lekstan [mailto:kuebzky@gmail.com]
> Sent: 25 November 2013 15:55
> To: user@zookeeper.apache.org
> Subject: Re: Disqualify a node from leader election
> 
> If I understand you correctly as you want the specific node never become
> the leader.
> 
> The best solution would be to configure your cluster into 2 groups, put
first 4
> servers into group 1 with weight 10 and 5th server into group 2 with
weight 0.
> This way 5th servers never gets elected as a leader.
> 
> http://zookeeper.apache.org/doc/trunk/zookeeperHierarchicalQuorums.ht
> ml
> 
> 
> 2013/11/25 FPJ <fpjunqueira@yahoo.com>
> 
> > D and E can only become a leader if they can form a quorum with B
> > and/or C (assuming you've taken A down). In the case A, D, E are the
> > only 3 servers able to talk to each other, killing A is going to make
> > you lose quorum, and if you bring A back up, it might be elected
> > again, so you might end up in this cycle until the net partition is
healed or B
> and/or C are up.
> >
> > I suppose we could have an option that tells servers to ignore a given
> > server when electing a leader, but it is not entirely trivial because
> > A in the example Ben gave might be the only available server that has
> > the latest committed txn. We would need a mechanism to transfer state
> > from a follower to a prospective leader.
> >
> > -Flavio
> >
> > > -----Original Message-----
> > > From: Benjamin Reed [mailto:breed@apache.org]
> > > Sent: 25 November 2013 01:21
> > > To: user@zookeeper.apache.org
> > > Subject: Re: Disqualify a node from leader election
> > >
> > > camille really has the right solution. you have to let it become the
> > leader and
> > > then kill it. here is why:
> > >
> > > lets says you have servers: A, B, C, D, and E and A is the node that
> > > you
> > don't
> > > want to be the leader. let's also say that C is a leader and commits
> > transaction
> > > x on A, B, and C but before D and E get x B and C fail. now A is the
> > > only surviving node with x, so unless A can become the leader, at
> > > least temporarily, D and E will never get x. if you follow Camille's
> > suggestion,
> > you
> > > let A become the leader (since it has the most recent
> > > transaction) and D and E will sync with A and get x. now if you
> > > restart
> > A,
> > > leader election will run again and D or E can be elected leader.
> > > this
> > does
> > also
> > > show that you want the less desirable nodes to have lower server ids
> > > so
> > that
> > > there will be less chance of them becoming leader if there is a "tie"
> > (other
> > > nodes are just as uptodate as them).
> > >
> > > ben
> > >
> > >
> > > On Sun, Nov 24, 2013 at 5:09 PM, Owen Kim <ohechkay@gmail.com>
> wrote:
> > >
> > > > Observers can't vote in leader election, though right? I'm not
> > > > sure the loss of fault tolerance would be worth it.
> > > >
> > > > The scenario is that I have a 5-node cluster but one node is in an
> > > > network partition that gets DOSed around it. When this happens and
> > > > it's leader, I see huge performance degradation. The real solution
> > > > is obviously to move the node off that network but I wondered if
> > > > there was an easy way to keep it from being leader in its
configuration.
> > > >
> >
> >


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