How to limit the number of connections on the level of the DB user / Database in the Postgres Server?

ALTER USER my_db_user WITH CONNECTION LIMIT 2;

SELECT rolname, rolconnlimit
FROM pg_roles
WHERE rolconnlimit <> -1;

This query will return nothing if you don't have any custom roll limits set up.

postgres=> select datconnlimit from pg_database where datname='my_database';
 datconnlimit 
--------------
            0
(1 row)

postgres=> alter database my_database connection limit -1;
ALTER DATABASE
postgres=> \q

dmitryr@dmitryr-mac my_postgres %