On Tue, Apr 22, 2014 at 2:06 PM, Dominique Devienne <[email protected]>wrote:
> Regarding the uniqueness argument made by DRH, it's actually very hard > to generate 2 random-based GUIDS [that collide], given that a 128-bit is a > very very > large number. > This is called the "Birthday Paradox". Ask Google for more information. To a good approximation, if there are N possible values, you need to generate sqrt(N) of them before you have a 50/50 chance of getting a collision. (Wikipedia has the exact formula, if you are interested, but the approximation is usually good enough.) So for a 128-bit GUID, you'd expect to get a collision after generating 4 billion of them, or so. The above assumes you have a good source of randomness. The "rand()" function in your favorite programming language is often not quite that good. But random() in SQLite does a decent job, at last on Unix where it can be seeded using /dev/random. -- D. Richard Hipp [email protected] _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
