server dropping connection

All,

I've been trying to run a nested query via a browser using a php script.
The script looks at a table with a couple years worth of data (6M rows).
If I constrain the search to five or six days of the data it works fine
and displays the result set in the browser, but if I have it parse the
entire table it errors out with this message:

server closed the connection unexpectedly This probably means the server
terminated abnormally before or while processing the request.

The error points at line 33, which is the $query = "SELECT..." in the
script.
The full table query runs fine in psql and the very limited query runs
fine in the php script so I'm thinking there might be some type of
resource starvation or client connection timeout happening. In psql the
full query over two years of data returns a result set (limit 50) in about
three minutes. Any ideas where I should begin looking?

thanks,

r