Quoting wickro <robwickert@gmail.com>:
> I have a largish table (> 8GB). I'm doing a very simple single group
> by on.
This doesn't answer your question, but you might want to take
advantage of table partitioning:
http://www.postgresql.org/docs/8.3/interactive/ddl-partitioning.html
I've recently gone through this exercise (several tables were 10GB+,
some almost 30GB) and if your WHERE clauses qualify, then expect
significant performance gains with /much/ better memory consumption.
You only have one large table, so partitioning it should be painless
and not take too long (unlike our scenario).
Cheers
Henry