How to determine whether I'm running on a standby?

Hi!

I am running PostgreSQL 13.5, one primary cluster and two standby
clusters, managed by PgBouncer which will automatically promote one of
the  standbys to the primary in case of failure. I have a job that is
cleaning "old data",  with "old data" being whatever business side of
the company deems as "old data". The cleanup is a PgPL/SQL procedure
which uses a bunch of DELETE commands. The procedure works fine on the
primary but reports a bunch of errors on the read-only standbys. In
another database system, I have the table called V$DATABASE and the
column named DATABASE_ROLE which can be either primary or some kind of
standby (physical or logical). Is there anything like that in the world
of Postgres? I would like to do something like this:

DECLARE

DB_ROLE VARCHAR2(64);

BEGIN

SELECT DATABASE_ROLE INTO DB_ROLE FROM V$DATABASE;

IF DB_ROLE = 'PRIMARY' THEN

   <do a bunch of deletions>

ELSE

    exit;

END IF;

END;

What would a similar idiom in the PostgreSQL world look like? I have the
job in crontab on the primary and I don't really know which of the 3
clusters will be my primary at any given moment. So far, I am using
manual labor to do that, which is silly. Knowing Postgres idioms, there
will probably be a function for this but I was unable to figure out
which one.

Regards

--
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com