Numerous prepared transactions?

Hi,

Is it viable to have very many prepared transactions? As in tens of
thousands or even more?

The idea is so that a web application can do _persistent_
transactional stuff over multiple pages/accesses/sessions and have it
rolled back easily, or committed if desired. I'm thinking that it
might be better to do this instead of reinventing transactions at the
application layer.

Would it be better to have separate postgresql databases for this?
One for the persistent transactions stuff, and one for "normal"
stuff, which will manage the persistent transactions.

Regards,
Link.