> It's clear to me where this should be set, but not at all clear where I
> can set the size of this pages. I have 10,000 for my
> DATABASE_CACHE_PAGES and I can see that my page size is 4096, I just
> have no idea how to change it, say to 8192.

There are several ways how to change number of cache pages, see
http://www.volny.cz/iprenosil/interbase/ip_ib_cache.htm

Page size can be set only when new database file is created, i.e.
either when creating new database (e.g. "Create Database '...' Page_Size 8192"
or isc_create_database(...)), or when restoring database from backup, see
http://www.volny.cz/iprenosil/interbase/gbak_switches.htm
for list of GBak switches.

Ivan