On 05-10-2010 20:39, Michael Gundlach wrote: >> I agree with Jay's comments elsewhere in this thread -- it seems a >> better idea to use a UUID for your internal_id, rather than a long >> int. That way, the ID is an extra 64 bits longer, so you can >> generate them randomly on independent nodes without worrying about >> collisions. > I think we discussed this in IRC -- 128 bits turns into a 26 byte > EC2 ID vs 14 for a 64 bit int, and someone (Soren?) had a strong > negative preference.
If I did, I think I'm over it now :) > Actually, I just checked in code only using a 32 bit integer, and > I'd like some convincing that this isn't sufficient for the > foreseeable future. I can provide that. :) > We want to support 1 million instances, right? Which is 1/4000 the > keyspace, so we have something like a 1 in 4000 chance of a > collision once we hit a million instances. Mm... Not exactly. 1/4000 is the chance of collision for the last one, assuming an even distribution. You reach a 1/4000 chance of having had *a* collision before you even start 150 instances. After a million instances, that figure grows to 99.99999999999999999999999999999999999999999999999999% or thereabouts. We're in 99% territory after a measly 200,000 instances. -- Soren Hansen Ubuntu Developer http://www.ubuntu.com/ OpenStack Developer http://www.openstack.org/
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