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From Camille Fournier <skami...@gmail.com>
Subject Re: locking/leader election and dealing with session loss
Date Wed, 15 Jul 2015 19:04:45 GMT
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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