The pg_stat_activity
table can be used to determine what connections there
currently are to the PostgreSQL server and to a particular database. To see
the process ids and usernames of all connection to your PostgreSQL server,
run the following query:
> select pid, usename from pg_stat_activity;
pid | usename
-------+------------
57174 | jbranchaud
83420 | jbranchaud
Include datname
in the requested columns to figure out the database of
each connection.
> select pid, usename, datname from pg_stat_activity;
pid | usename | datname
-------+------------+-----------
57174 | jbranchaud | hr_hotels
83420 | jbranchaud | pgbyex
The results can be restricted to a particular database as necessary.
> select pid, usename from pg_stat_activity where datname = 'hr_hotels';
pid | usename
-------+------------
57174 | jbranchaud