Some time ago, I promised to write about some of the techniques used in Oracle. A very early draft of a paper on Multi-Version concurrency is now available. It discussed MVCC implementations in PostgreSQL and Oracle.
SimpleDBM does not implement MVCC on purpose, as I wanted to understand traditional implementations before attempting to implement MVCC. Perhaps one day, a different version of SimpleDBM will implement MVCC.
I am very keen on ensuring that this paper is accurate in its description of PostgreSQL and Oracle implementations. I would also like to add descriptions of other DBMSes like Firebird and MySQL/InnoDb.