mysql's "replace into..."

Hi all,

I'm in the process of migrating a production database and related
applicatoins from mysql to postgresql.  I've just not been very impressed
with mysql's stability, that is I'm trying to make my phone stop ringing.

However, when I wrote the applications, I took free advantage of mysql's
replace into feature which behaves like a smart insert that inserts new
records or updates old records.  I'm using perl DBI and need to figure out a
good way to migrate this to postgresql. 

Any ideas?

Mike Diehl.