On Tue, Oct 5, 2010 at 2:31 PM, Ewan Mellor <[email protected]>wrote:
> Thanks Michael. It would be great to see this in some doccomments in the > code somewhere. > Yeah, I agree -- I first touched this code to rename ec2_id to internal_id, and it's been a bit of a pain because there's a dearth of comments (and some ambiguous naming, like "instance_id" referring to id in some places and to ec2_id in other places.) I plan to clean this code up as one of my post-FF tasks. > 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. 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. 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. I know I'm not doing the statistics properly, since the proper question is "what is the chance of at least one collision when successively generating one million random 32-bit integers?", but it feels like we can punt on larger values at least until Bexar. Thoughts? Michael Confidentiality Notice: This e-mail message (including any attached or embedded documents) is intended for the exclusive and confidential use of the individual or entity to which this message is addressed, and unless otherwise expressly indicated, is confidential and privileged information of Rackspace. Any dissemination, distribution or copying of the enclosed material is prohibited. If you receive this transmission in error, please notify us immediately by e-mail at [email protected], and delete the original message. Your cooperation is appreciated.
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