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From Jeremiah Jordan <>
Subject Re: How to reliably achieve unique constraints with Cassandra?
Date Fri, 06 Jan 2012 22:08:15 GMT
By using quorum.  One of the partitions will may be able to acquire 
locks, the other one won't...

On 01/06/2012 03:36 PM, Drew Kutcharian 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<>  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

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