Обсуждение: 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

On Thu, Feb 10, 2022 at 12:54 PM Mladen Gogala <gogala.mladen@gmail.com> wrote:

The procedure works fine on the primary but reports a bunch of errors on the read-only standbys.

A standby is in perpetual recovery mode.