[ntoshev]

No idea how pg handles it, but here is an easy do-it-yourself way: http://armstrongonsoftware.blogspot.com/2006/09/pure-and-sim...

It doesn't matter it is in Erlang - you can do it in any language. A Lisp that implements software transactional memory is Clojure (runs on the JVM): http://clojure.sourceforge.net/