For those who might be interested I started documenting some of the JDBM partition implementation details here:

    http://cwiki.apache.org/confluence/display/DIRxSRVx11/JDBM+Partition+Design

It's a work in progress and so I will document as I go along with the Cursor refactoring.  Consider this official since everything else we have about this is outdated or just simply incorrect. 

Alex