postgresqlsession

Handle session storage with PostgreSQL

I'm making a login system for an application where there will not be many users. I figured I'd store sessions as 4-byte integers, as that'd be far more than enough.

Basic idea:

session_id INTEGER NOT NULL DEFAULT (random() * 4294967295 - 2147483648)

I.e., the database creates a more or less random number, which is used as primary key, and identifier for the session.

Is there an obvious pitfall with this sort of approach?
What happens if there's a collision? I'd imagine it tries again, but does it?
There should be no risk of the table filling up, but what'd happen if it were about to run out of unique numbers?

I also looked at definitions like GENERATED ALWAYS AS IDENTITY or GENERATED ALWAYS AS(expression) STORED, but I don't want a sequence, and those seem to require immutable functions, and random() isn't apparently immutable. Is there a way to implement them with this sort of approach?

I did some preliminary testing and my basic idea seems to work. But I'm unsure if it's good on the long run.

Solution
    1. session_id BIGINT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY - this strictly guarantees and enforces uniqueness. If someone attempts to insert the same session_id for the second time or update...set another one to introduce a duplicate, it'll get rejected with an error.
    2. Random() with two constants only make uniqueness likely. Given enough time/attempts, it's therefore guaranteed to break.
    3. Without adding unique or primary key, you're not enforcing it at all - nothing's watching out for collisions, nothing reports them, they are free to occur.
    4. You can always run out of numbers, but with bigint and uuid there's a lot to run out of. Unless that's a seriously large project, other things will typically break sooner than you manage to exhaust them.
    5. If you want non-sequential identity, use uuid: 
      session_id uuid default gen_random_uuid() PRIMARY KEY
    6. If you're worried about identifiers being sequential, it might be because you're exposing them, which you shouldn't do even if they are not sequential.