controlling process priority

Hi--

I've got a complicated SQL select/insert which inserts up to 1 million
records when run and can take up to 20 minutes to complete. Is there a way
to control the priority of this select such that when Postgres is busy with
other (higher priority) tasks it gets delayed??

My problem is that when dealing with lots of traffic, if one of these
complex queries gets run, all the query traffic is slowed considerably thus
hurting the performance of my application.

Thanks,

Peter T. Brown