Paolo and I are starting work on transactions for TDB.
This is sufficiently complicated we're going to write the design up, then prototype then do the final implementation.
The write-up is starting at: https://cwiki.apache.org/confluence/display/JENA/TxTDB (and it's unfinished) It's based on write-ahead logging. See also: https://issues.apache.org/jira/browse/JENA-41 which is "Multiple Reader AND Single Writer" concurrency for TDB. Andy
