In response to Scott Ribe <scott_ribe@xxxxxxxxxxxxxxxx>: > On Jan 5, 2011, at 1:31 AM, RadosÅaw Smogura wrote: > > > * simple to generate, and 128bit random is almost globally unique, > > Almost? Should be totally unique, as long as your random source is decent quality. This is going off-topic, but I did some research on this because we were considering using UUIDs for various keys ... Fact is, UUIDs are not _guaranteed_ to be unique. If you use the generating system that includes a MAC address, then in theory, they are guaranteed to be unique, but in practice, MAC addresses aren't guaranteed to be unique either, so that's not 100% either. Beyond that, the namespace size for a UUID is so incomprehensibly huge that the chance of two randomly generated UUIDs having the same value is incomprehensibly unlikely ... it is, however, not a 100% guarantee. Anyway, in our case, we determined that the chance of UUID collision for the dataset in question was extremely unlikely, however, the consequences of such a collision were pretty bad. We also determined that we were able to control a "unit ID" for each independent system that would generate IDs, which could (a) be part of a unique seed for UUIDs, or (b) be a prefix to a autonumber ID that would be a lot easier to read and work with manually. In the end, we chose b for the human factor. Face it, reading, remembering, and typing UUIDs kinda sucks. -- Bill Moran http://www.potentialtech.com http://people.collaborativefusion.com/~wmoran/ -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
