Deletion of availability data goes

delete from rhq_availability where end_time < ?

Without an index, the database is doing a full table scan which can be extremely expensive

With the index, the database can use the index and can do an index range scan.

rhq300=# explain delete from rhq_availability where end_time < 12345678
rhq300-# ;
                           QUERY PLAN                           
----------------------------------------------------------------
 Seq Scan on rhq_availability  (cost=0.00..9.76 rows=1 width=6)
   Filter: (end_time < 12345678)
(2 rows)

rhq300=# create index end_time_index ON rhq_availability (end_time );
CREATE INDEX
rhq300=# explain delete from rhq_availability where end_time < 12345678
;
                                      QUERY PLAN                                       
---------------------------------------------------------------------------------------
 Index Scan using end_time_index on rhq_availability  (cost=0.00..8.27 rows=1 width=6)
   Index Cond: (end_time < 12345678)
(2 rows)