increase performance

Hi

I use Jahia 4.02 with Oracle 8i, and it's quite slow : it takes 3 seconds for each user at the first call of a page (simple template, just to read). On edition side, it takes sometimes 7 seconds to publish a page (simple template)...
In the mailing - list, I read it's a matter of indexes - I haven't found any one on Oracle - which index should we create ?
What about the caches -  should I flush one of them ?

Thanks for answer