large number of files open...

i'm running postgres 7.1.3 in a production environment. the database 
itself contains on the order of 100 tables, including some complex 
triggers, functions, and views. a few tables (on the order of 10) that 
are frequently accessed have on the order of 100,000 rows.

every now and then, traffic on the server, which is accessed publicly 
via mod_perl (Apache::DBI) causes the machine itself to hit the kernel 
hard limit of number of files open: 8191.

this, unfortunately, crashes the machine. in a production environment of 
this magnitude, is that a reasonable number of files to expect postgres 
to need at any given time? is there any documentation anywhere on what 
the number of open files depends on?

-tfo