https://www.postgresql.org/docs/current/explicit-locking.html
https://postgrespro.ru/docs/postgresql/current/explicit-locking
https://pglocks.org/?pgcommand=VACUUM

samples
select ... for update;

select ..., pg_blocking_pids(pid), ...
from pg_stat_activity
where
    backend_type = 'client backend';

pg_locks
    transactionid, granted

pg_terminate_backend(pid)
    function