I would like to find a Lisp database interface that is. I intend to build a general ODBMS layer in lisp on top of such. To do so I need
make sure to check out cl-perec and cl-rdbms. perec aims to be an sql based transparent persistency layer on CLOS - transparent to the extent it's feasible.
YMMV and there's not much documentation, but there are tons of tests and it's used in a production system (as a backend for a webapp).
we are using cl-postgres (part of postmodern) and we had no problem with multithreaded use.