On Mon, Jan 24, 2011 at 11:21 AM, Duquette, William H (318K) < william.h.duque...@jpl.nasa.gov> wrote:
> A question on using randomblob(16) to generate UUIDs, as the SQLite docs > suggest: what assurance do you have that the UUID really is universally > unique? It's a pseudo-random number, and you can replicate a stream of > pseudo-random numbers by setting the seed appropriately. Is randomblob() > doing some kind of magic in its seeding of the random number stream? > The SQLite PRNG is based on RC4 and is quite good. On unix, it is seeded from /dev/random (where available - which is pretty much everywhere these days, except on windows). So if you do the math, you'll see that the odds of getting duplicate randomblob(N) (for suitably large N, say 20) are far smaller than a giant meteor striking earth and ending all life here. So while it is mathematically possible, we consider it sufficiently unlikely that it can be disregarded. > > Will > > > On 1/24/11 3:49 AM, "Alexey Pechnikov" <pechni...@mobigroup.ru> wrote: > > See > http://sqlite.mobigroup.ru/dir?name=ext/uuid > > 2011/1/24 sqlite-us...@h-rd.org <sqlite-us...@h-rd.org> > > > Hi, > > > > I have put together a simple uuid generation method in sqlite: > > > > select '{' || hex( randomblob(4)) || '-' || hex( randomblob(2)) > > || '-' || '4' || substr( hex( randomblob(2)), 2) || '-' > > || substr('AB89', 1 + (abs(random()) % 4) , 1) || > > substr(hex(randomblob(2)), 2) || '-' || hex(randomblob(6)) || > > '}'; > > > > It's based on the description for v.4 uuid's in wikipedia > > https://secure.wikimedia.org/wikipedia/en/wiki/Uuid . > > > > But I am thinking there may be a better (or another) method to do this > > in sqlite, without the need to use something external? > > > > thanks > > > > _______________________________________________ > > sqlite-users mailing list > > sqlite-users@sqlite.org > > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > > > > > > -- > Will Duquette -- william.h.duque...@jpl.nasa.gov > Athena Development Lead -- Jet Propulsion Laboratory > "It's amazing what you can do with the right tools." > > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
