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From Alexander Shraer <shra...@gmail.com>
Subject Re: locking/leader election and dealing with session loss
Date Wed, 15 Jul 2015 19:08:21 GMT
+1 to what Camille is saying & suggestion to use generations

On Wed, Jul 15, 2015 at 12:04 PM, Camille Fournier <skamille@gmail.com>
wrote:

> If client a does a full gc immediately before sending a message that is
> long enough to lose the lock, it will send the message out of order. You
> cannot guarantee exclusive access without verification at the locked
> resource.
>
> C
> On Jul 15, 2015 3:02 PM, "Jordan Zimmerman" <jordan@jordanzimmerman.com>
> wrote:
>
> > I don’t see how there’s a chance of multiple writers. Assuming a
> > reasonable session timeout:
> >
> > * Client A gets the lock
> > * Client B watches Client A’s lock node
> > * Client A gets a network partition
> > * Client A will get a SysDisconnected before the session times out
> > * Client A must immediately assume it no longer has the lock
> > * Client A’s session times out
> > * Client A’s ephemeral node is deleted
> > * Client B’s watch fires
> > * Client B takes the lock
> > * Client A reconnects and gets SESSION_EXPIRED
> >
> > Where’s the problem? This is how everyone uses ZooKeeper. There is 0
> > chance of multiple writers in this scenario.
> >
> >
> >
> > On July 15, 2015 at 1:56:37 PM, Vikas Mehta (vikasmehta@gmail.com)
> wrote:
> >
> > Camille, I don't have a central message store/processor that can
> guarantee
> > single writer (if I had one, it would reduce (still useful in reducing
> lock
> > contention, etc) the need/value of using zookeeper) and hence I am trying
> > to
> > minimize the chances of multiple writers (more or less trying to
> guarantee
> > this) while maximizing availability (not trying to solve CAP theorem), by
> > solving some specific issues that affect availability.
> >
> >
> >
> > --
> > View this message in context:
> >
> http://zookeeper-user.578899.n2.nabble.com/locking-leader-election-and-dealing-with-session-loss-tp7581277p7581284.html
> > Sent from the zookeeper-user mailing list archive at Nabble.com.
> >
>

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