Replacing sequence with random number

Question

I would like to replace some of the sequences I use for id\'s in my postgresql db with my own custom made id generator. The generator would produce a random number with a ch

Answer 1

For generating unique and random-looking identifiers from a serial, using ciphers might be a good idea. Since their output is bijective (there is a one-to-one mapping between input and output values) -- you will not have any collisions, unlike hashes. Which means your identifiers don't have to be as long as hashes.

Most cryptographic ciphers work on 64-bit or larger blocks, but the PostgreSQL wiki has an example PL/pgSQL procedure for a "non-cryptographic" cipher function that works on (32-bit) int type. Disclaimer: I have not tried using this function myself.

To use it for your primary keys, run the CREATE FUNCTION call from the wiki page, and then on your empty tables do:

ALTER TABLE foo ALTER COLUMN foo_id SET DEFAULT pseudo_encrypt(nextval('foo_foo_id_seq')::int);

And voila!

pg=> insert into foo (foo_id) values(default);
pg=> insert into foo (foo_id) values(default);
pg=> insert into foo (foo_id) values(default);
pg=> select * from foo;
  foo_id   
------------
 1241588087
 1500453386
 1755259484
(4 rows)