> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:owner-u2- > [EMAIL PROTECTED] On Behalf Of Anthony W. Youngman > Sent: Saturday, April 26, 2008 9:14 AM > To: u2-users@listserver.u2ug.org > Subject: Re: [U2] Guaranteed unique sequential keys > > In message <[EMAIL PROTECTED]>, Glen B > <[EMAIL PROTECTED]> writes > > It's not overkill if you need a multi-app/multi-process service that > offers > >a single source for sequential keys. The other option is disk file > locking. > >Any way you look at it, you have to go to one place for the key. Don't > relay > >on O/S random numbers either. Even those are flawed at high resolution. > > Ummm.... > > My first reaction to this was "linux has a guaranteed true random number > generator" - the only problem is that if it runs out of randomness it > simply stops generating and anything asking for a number has to wait. > > Oh - and what do you mean by "high resolution"? I think that, if you > have a true random number generator, the chances of having a collision > approach 50% when you've used only 10% of the number space. (The classic > question about this is "how many people do you need in a room to have > even odds that two of them will share a birthday?". I think the answer > is "about 20".) >
That is true and what I mean by high resolution is extremely frequent requests. The scale of that is dependant on the hardware and the application making the requests. When the entropy pool runs out, you get a function block until more hardware data is available to generate a new value. That is what I mean by "flawed". If you have a tiny box with a small entropy pool, you could exhaust the entropy pool often which could lead to performance issues. Of course, the new pseudo generators don't block at all. That is what you are referring to below. The problem there is that entropy pool is reused to generate pseudo bits to regenerate new keys from, which increases the chance of repeated keys. > But then, if you want unique, pseudo-random keys, I think there are > generators that are guaranteed to return every possible number, only > once, each cycle through the number space. > > None of this, however, solves the OP's original problem, I don't > think... > > Cheers, > Wol That's true. Random keys can not be sorted by order of creation. Glen ------- u2-users mailing list u2-users@listserver.u2ug.org To unsubscribe please visit http://listserver.u2ug.org/
