How to detect query which holds the lock in Postgres?

Question

I want to track mutual locks in postgres constantly.

I came across Locks Monitoring article and tried to run the following query:

SELECT bl.pid     A         


        

Answer 1

Since 9.6 this is a lot easier as it introduced the function pg_blocking_pids() to find the sessions that are blocking another session.

So you can use something like this:

select pid, 
       usename, 
       pg_blocking_pids(pid) as blocked_by, 
       query as blocked_query
from pg_stat_activity
where cardinality(pg_blocking_pids(pid)) > 0;