>> Don't you need to update main database file to put a "label" that
>> database is in "nbak"-like mode? I guess some more functionality is
>> needed...
> Yes, but the database may be burned to CD already locked. The
> application will need to be installed on a fixed path.
>
> What I don't know is if the engine will open the file on the CD
> (read-only) and the delta in read-write mode.

So, in fact we have two requirements:

a) allow opening delta-file in read-write mode even if main database is
opened in read-only mode;

b) allow specifying a custom path for deltas in the firebird.conf file.

The only drawback of this scheme is that there are no chances of
nbak-ing the delta with nbak. But I think this is quite acceptable for
this use case, since we're talking about embedded use where main
database is bigger than delta.

BTW, what about garbage collection in the delta?

Somebody cares to post a summary of this feature to user newsgroups to
check whether there is need for such feature (possibly asking replying
only those, who are ready to provide some financing for this particular
feature).

Roman