On 01/05/2011 08:55 AM, Bill Moran wrote: > In response to Scott Ribe <scott_r...@elevated-dev.com>: > >> On Jan 5, 2011, at 8:05 AM, Bill Moran wrote: >> >>> 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 >> >> Yes, as in: it is *far* more likely that all of your team members and all of >> your client contacts will be simultaneously struck by lightning and killed >> in their sleep, and it is *far* more likely that all life on earth will be >> wiped out by an asteroid impact, and it is *far* more likely that the solar >> system orbits are not actually stable and earth will fly off into space... >> If you're worried about UUID collisions, then either your priorities are >> completely wrong, or you live in a bomb shelter--that's not sarcasm by the >> way, it's simply true, the chance of a collision is so vanishingly small >> that it is dwarfed by all sorts of risks that we all ignore because the >> chances are so low, including the chance that all drives in all your RAIDs >> across all your replicas will simultaneously fail on the same day that fires >> start in all the locations where your tapes are stored and all the sprinkler >> systems fail... (By "far" more likely, I mean many many many orders of >> magnitude...) > > That statement demonstrates a lack of investigation and/or consideration > of the circumstances. > > I can't find my math or I'd reproduce it here, but consider this: > > If you have 50 devices, each generating 100 UUIDs per hour, and you'll > keep records for 1 year, then your argument above is probably accurate. > > However, if there are 5000 devices generating 100 UUIDs per hour, and you'll > be keeping those records for 10+ years, the chances of collisions near > the end of that 10 year span get high enough to actually make developers > nervous. >
But we're talking about a primary key. Postgres guarantees the uniqueness. 1 transaction in 10^^100 rolls back due to a second instance of an (otherwise/almost) uuid. Big deal. -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
