Thank You all for your advice.
You bet I learned the vacuum lesson, but the fact is that I'm running several servers (with postgresql 7.1 and oacs 3.x) wich perform at lightning speed even if I run vacuum analyze only when I remember to do so.
One argument I have always used in favor of PostgreSQL against Oracle was that it didn't require me to spend more than one hour per year in DB tuning: it seems that combining oacs.4.x with PostgreSQL 7.2.x will require more, but oacs.4.x is so rewarding to fully justify these complications.
