Pierre-
Reading from the tables is very fast, what bites you is that postgres
has to convert the data to wire format, send it to the client, and the
client has to decode it and convert it to a format usable by your
application. Writing a custom aggregate in C should be a lot faster
since it has direct access to the
data itself. The code path from actual table data to an aggregate is
much shorter than from table data to the client...
I think your comments really get at what our working hypothesis was, but
given that our experience is limited compared to you all here on the
mailing lists we really wanted to make sure we weren't missing any
alternatives. Also the writing of custom aggregators will likely
leverage any improvements we make to our storage throughput.
Thanks,
Nick