>>>It's very surprising that no one seems to have solved such a common use case. I would say people have solved it using RIGHT tools for the task.
On Fri, Jan 6, 2012 at 2:35 PM, Drew Kutcharian <d...@venarc.com> wrote: > Thanks everyone for the replies. Seems like there is no easy way to handle > this. It's very surprising that no one seems to have solved such a common > use case. > > -- Drew > > On Jan 6, 2012, at 2:11 PM, Bryce Allen wrote: > > > That's a good question, and I'm not sure - I'm fairly new to both ZK > > and Cassandra. I found this wiki page: > > http://wiki.apache.org/hadoop/ZooKeeper/FailureScenarios > > and I think the lock recipe still works, even if a stale read happens. > > Assuming that wiki page is correct. > > > > There is still subtlety to locking with ZK though, see (Locks based > > on ephemeral nodes) from the zk mailing list in October: > > > http://mail-archives.apache.org/mod_mbox/zookeeper-user/201110.mbox/thread?0 > > > > -Bryce > > > > On Fri, 6 Jan 2012 13:36:52 -0800 > > Drew Kutcharian <d...@venarc.com> wrote: > >> Bryce, > >> > >> I'm not sure about ZooKeeper, but I know if you have a partition > >> between HazelCast nodes, than the nodes can acquire the same lock > >> independently in each divided partition. How does ZooKeeper handle > >> this situation? > >> > >> -- Drew > >> > >> > >> On Jan 6, 2012, at 12:48 PM, Bryce Allen wrote: > >> > >>> On Fri, 6 Jan 2012 10:03:38 -0800 > >>> Drew Kutcharian <d...@venarc.com> wrote: > >>>> I know that this can be done using a lock manager such as ZooKeeper > >>>> or HazelCast, but the issue with using either of them is that if > >>>> ZooKeeper or HazelCast is down, then you can't be sure about the > >>>> reliability of the lock. So this potentially, in the very rare > >>>> instance where the lock manager is down and two users are > >>>> registering with the same email, can cause major issues. > >>> > >>> For most applications, if the lock managers is down, you don't > >>> acquire the lock, so you don't enter the critical section. Rather > >>> than allowing inconsistency, you become unavailable (at least to > >>> writes that require a lock). > >>> > >>> -Bryce > >> > > -- Narendra Sharma Software Engineer *http://www.aeris.com <http://www.persistentsys.com>* *http://narendrasharma.blogspot.com/*
