basic question about user-/role concept in postgres-databases
There are basically two choices:


Your application does the user and permission management itself. Then it typically has a single &ldquo;application user&rdquo; in the database.
Your application has per-user or per-group database users and handles user and permission management with database means.


Both solutions are fine. The second solution is maybe less commendable if you have lots of users; also, connection pooling usually works better with the first technique.

If you use database users like in the second solution, you should use NOLOGIN roles (user groups) in PostgreSQL to carry the permissions, and you assign the named users to the groups as appropriate. That way you don't have to GRANT and REVOKE a lot of permissions whenever you add or remove a user or change a user's role in the application.

To answer your question, there are no restrictions on concurrency with different database users.