Re: DB connection issue suggestions

If the problem occurs gradually (like leaking 20 connections per hour during
ETL), you can check pg_stat_activity every hour or so to try to observe the
problem before all the connection slots are used up, to collect diagnostic
information.

Alternately, leave a connection opened to the DB and wait until all connection
slots *are* used up, and then check pg_stat_activity.  That will take longer,
and you'll have more information to weed through.

What messages are in the server's log ?

v11.2 is years old and hundreds of bugfixes behind.  Since you ran into this
problem anyway, why not run 11.16, which was released today ?

How did you install postgres 11 ?  From source or from packages ?  Which
packages ?  The semi-official PGDG RPM packages are available here:
https://yum.postgresql.org/

-- 
Justin