[plt-scheme] data persistence

Currently I do data persistence (e.g. in a servlet) by serializing
entire data structures to disk every time they're changed.  I'd like
to do something a little less brute-force, e.g. just write deltas and
only occasionally save the whole thing.  I don't think I'm ready to
move up to a full-scale database server, so I'm staying away from
spgsql/schemeql for now.  Does anyone have anything in between?

--dougo at place.org