[reposting as the original seemed to get lost in a mail system issue on my end. Sorry if it did make it.] Hi This must be a fairly common requirement, but either I don't know how to ask Google about it or there's not as much out there as I would've expected. At a high level, what I need is a way to "scramble" sequences so it's not obvious that, say, customer 1332 is in fact the one-thousand-and-thirty-second customer of the company, because the next customer signed up might well get customer number 12, or 99442312. I'm hoping to do this with a mapping of values from a normal sequence, so that I can preserve the concurrency-friendly properties of normal sequences and not have to deal with the nightmare of gapless-sequence-like code. So: I'm looking for a way to map the output from a monotonically increasing sequence (not necessarily gapless - ie a normal Pg SEQUENCE) within a particular range into a random-looking different value in the same range with a 1:1 input->output relationship. In other words, for the 32 bit integer input of (say) "27" the output will always be the same (say 32 bit) number, and no other input will produce that output. A reverse mapping is not necessary; I don't care about being able to find out what input produced the output (say) 41231. Note that I'm *NOT* looking for a PRNG that takes the previous output as its input. That'd force me to use the same techniques as for a gapless sequence in Pg, with all the associated horror with locking and deadlocks, the performance issues, etc. That, or use a C extension module (which I'd rather avoid for portability and future proofing) to provide sequence-like properties. Does anyone here know of a good algorithm to do this that doesn't just iterate `n' times through a PRNG with the same seed, but instead does a true non-colliding space mapping? If I find something good and there aren't any existing Pl/PgSQL implementations I'll post one for others' use, since I'm pretty sure it must come up a lot. You don't want your database to send out "invoice #1" or "customer #1" after all. (I'm also going to be looking for efficient ways to calculate effective check digits for arbitrary numbers within a certain range, too, and will post something for that, but that comes later). -- Craig Ringer -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
