[Dovecot] prefetch + static + deliver

Hi all...

The prefetch entry in the wiki says:

"If you're using Dovecot's local delivery agent, you'll still need a valid userdb which it can use to locate the users. You can do this by adding a normal sql/ldap userdb after userdb prefetch."

(http://wiki.dovecot.org/UserDatabase/Prefetch)

My question is:

Does it need to be a SQL/LDAP userdb? How about static or passwd?

Thanks in advance :)