This is a followup to #8565. With many long reports in the database (large messages and logs tables), expiring reports takes quite a long time on our machine. Sometimes more than a day so that multiple jobs sum up and start hogging the CPU. Here's how the situation looks like:

foreman=> select count(*) from reports;
 count
-------
  1951
(1 row)

foreman=> select count(*) from messages;
 count
--------
 704462
(1 row)

foreman=> select count(*) from logs;
 count
--------
 802815
(1 row)

foreman=> explain DELETE FROM "messages" WHERE (id not IN (SELECT DISTINCT message_id FROM "logs" ));
                                                         QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------
 Delete on messages  (cost=0.42..9806323789.43 rows=352231 width=6)
   ->  Seq Scan on messages  (cost=0.42..9806323789.43 rows=352231 width=6)
         Filter: (NOT (SubPlan 1))
         SubPlan 1
           ->  Materialize  (cost=0.42..27142.52 rows=279366 width=4)
                 ->  Unique  (cost=0.42..24653.69 rows=279366 width=4)
                       ->  Index Only Scan using index_logs_on_message_id on logs  (cost=0.42..22646.65 rows=802815 width=4)
(7 rows)