Trying to Tunning DB

Hi,

I'm doing a project and I've have some problems.

My table has (ID, atr1,..., atn), but there isn't any primary key because of the specifications, it's very similar to a Data warehouse, where every event is stored. It hasn't any delete, only inserts (more than 10^7) and many updates.

The thing is that it takes too much time in execute. (In my case, before each update I've to do select to find which row I have to modify, and I suppose it does a table scan. To improve it, I've thought to use a Btree for ID column).

I use JDBC. To make it works better, I use:

a.. Prepared Statements,
b.. setAutocommit(false), ( in my case I don't need transactions).
c.. I'm been reading PostgreSQL mailing list archive to try to discover other kinds of "tune", or how to improve it.
d.. I've also read FAQ and I've found "3.6) How do I tune the data base engine for better performance".
But in my case, would you think vacuum and analyze are good options? Can I do everything else? Can I also disable the catalog?

Thanks a lot

yours,

Cris..