performnce problem

Hi everybody,

I'm having a serious performance problem. We're using PostgreSQL (7.1.3) for
data collection (appr. 3 000 000 new records per day). Every night all
records older than 3 days are deleted, after that a vacuumdb is done. The
table has about 7-8 M records and is about 2,5GB size on the file-system. I
noticed that the time consumed by vaccum increases from about 5 mins to 11
mins now within the last 5 weeks which I thought this happens because of
increased tables over the last weeks on the system.

The whole system worked well for several weeks now. Starting this night
everything slowed down. Simple SQL commands (Select date(dt),sum(bytes) from
table where source between 'xxx.xxx.xxx.xxx' and 'xxx.xxx.xxx.xxx' and dt >=
'10-30-2001' and dt < '10-31-2001 00:00:00' group by date(dt)) which are
done within a few seconds before take minutes now to compute... There were
no changes on the system the last times. The file-system has no errors.

PostgreSQL is installed on a RedHat 7.1 with Kernel 2.4.2-2. The hardware is
a PIII-500 with 256MB RAM and 10GB HD (IDE).

Does anyone has a idea what the reason could be and how it could be fixed?

Thanks in advance!

Martin