The page http://www.postgresql.org/about/ states:
"There are active PostgreSQL systems in production environments that
manage in excess of 4 terabytes of data."
This seems like an obsolete comment. There are single node databases
that Heroku controls that are larger than that now. I doubt Heroku
really pushes PostgreSQL to its limits in this dimension, and it seems
reasonable to suppose some production PostgreSQL databases are far
larger these days.
--
Regards,
Peter Geoghegan