Hanging Query

We have to inserts a records(15000- 20000) into a table which also
contains (15000-20000) records, then after insertion, we have to delete
the records according to a business rule.
Above process is taking place in a transaction and we are using batches
of 128 to insert records.
Everything works fine on QA environment but somehow after inserts,
delete query hangs in production environment. Delete query has some
joins with other table and a self join. There is no exception as we
have done enough exception handling. It simply hangs with no trace in
application logs.

When I do "ps aux" , I see
postgres 5294 41.3 2.4 270120 38092 pts/4 R 10:41 52:56
postgres: nuuser nm 127.0.0.1 DELETE

Postgres 7.3.4 on Linux..

Thanks for any help..

Vimal