select t1.datname AS db_name,
       pg_size_pretty(pg_database_size(t1.datname)) as db_size
from pg_database t1
order by pg_database_size(t1.datname) desc;

-- Check running processes:
SELECT * FROM pg_stat_activity WHERE state = 'active';

-- Find the process you want to kill, then type:
SELECT pg_cancel_backend(<pid of the process>);

-- If the process cannot be killed, try:
SELECT pg_terminate_backend(<pid of the process>)