Postgresql: Trigger is not working at times

Question

I have a PostgreSQL trigger that is not firing sometimes, even though the status is always shown as "enabled".

My trigger code is as follows:

CREATE OR REPLACE FUNCTION audit_src_exhibit() RETURNS trigger AS $BODY$
BEGIN
  IF TG_OP = 'INSERT' then
        if new.audit_created_date is null  THEN
        new.audit_created_date := current_timestamp;
        new.audit_created_by := session_user::text;
    end if;
    else
        if new.audit_modified_date is null  THEN
        new.audit_modified_date := current_timestamp;
        new.audit_modified_by := session_user::text;
    end if;
END IF;
  RETURN NEW;
END; $BODY$ LANGUAGE plpgsql VOLATILE;

CREATE TRIGGER audit_src_exhibit_tr
BEFORE INSERT OR UPDATE ON <table>
FOR EACH ROW EXECUTE PROCEDURE audit_src_exhibit();

Is there any specific reason for this behaviour?
Does my code show any signs of known issues which would result in triggers not firing?

I am getting the audit columns as empty even though some insert and update happened today

Answer 1

The NULL values for audit_created_date could be explained if the operation was an UPDATE, because your trigger doesn't modify audit_created_date in that case.

If those were INSERTs, then the only possible explanations would be

1. The trigger was not defined or disabled at the time the statements happened. To preempt the follow-up question: no, PostgreSQL doesn't disable triggers on its own.

2. session_replication_role was set to replica when the statements were executed. That will prevent firing of all except replica triggers. You can change that for a trigger with

   ALTER TABLE "<table>" ENABLE ALWAYS TRIGGER audit_src_exhibit_tr;