A better way would be to seed a Mersenne Twister PRNG at server startup time and then use the same generator for all subsequent calls. http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
The period is exceptionally long, and it has many excellent properties. > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of D. Stimits > Sent: Monday, October 04, 2004 7:23 AM > Cc: [EMAIL PROTECTED] > Subject: Re: [GENERAL] Random not so random > > > Tom Lane wrote: > > "Arnau Rebassa" <[EMAIL PROTECTED]> writes: > > > >> I'm using a debian linux as OS with a 2.4 kernel running on it. > > > > > >>>Incidentally, are you reconnecting every time or is it > that multiple > >>>calls > >>>in a single session are returning the same record? > > > > > >> I'm reconnecting each time I want to retrieve a message. > > > > > > Hmm. postmaster.c does this during startup of each backend process: > > > > gettimeofday(&now, &tz); > > srandom((unsigned int) now.tv_usec); > > If it uses the same seed from the connection, then all > randoms within a > connect that has not reconnected will use the same seed. > Which means the > same sequence will be generated each time, which is why it is > pseudo-random and not random. For it to be random not just the first > call of a new connection, but among all calls of new connection, it > would have to seed it based on time at the moment of query and not at > the moment of connect. A pseudo-random generator using the same seed > will generate the same sequence. > > D. Stimits, stimits AT comcast DOT net > > > ---------------------------(end of > broadcast)--------------------------- > TIP 8: explain analyze is your friend > ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
