postgresqlrandomprngentropy

Quality of PostgreSQL's random() function?

Let's say I'm creating a table foo with a column bar that should be a very large random integer.

CREATE TABLE foo (
    bar bigint DEFAULT round(((9223372036854775807::bigint)::double precision * random())) NOT NULL,
    baz text
);

Is this the best way to do this? Can anyone speak to the quality of PostgreSQL's random() function? Is the multiplication here masking the entropy?

Note that I do have good hardware entropy feeding into /dev/random.

Solution

  • Postgresql random is based on their own portable implementation of POSIX erand48. It's a linear congruential PRNG in a 48 bit domain.

    If you need something stronger look to the pg_crypto module's gen_random_bytes function which is used to produce cryptographically strong entropy.