Memory exhausted on DELETE.

I have a table with about 1,400,000 rows in it.  Each DELETE cascades to
about 7 tables.  When I do a 'DELETE FROM events' I get the following
error:

  ERROR:  Memory exhausted in AllocSetAlloc(84)

I'm running a default install.  What postgres options to I need
to tweak to get this delete to work?

Also, if my tables grows to 30,000,000 rows will the same tweaks
still work?  Or do I have to use a different delete strategy, such
as deleting 1000 rows at a time.

Thanks.