The unified codebase just committed to our Subversion repository is fully multithreaded and supports 2PL (two phased locking) and MVCC (multiversion concurrency control). The 2PL capabilities will be tested and completed first, leading to version 1.9. The MVCC capabilities will be completed next, and the unified version will be released as version 2.0.
A major rewrite of HSQLDB, the leading SQL database engine written in Java, has been done over the last 3 years. Support for very large, disk-based result sets, date-time arithmetic and the INTERVAL type, new query processor and optimiser, are among the features. We have been extending SQL Standard conformance, covering almost full SQL-1992 language features and extensive SQL:2009 optional features.
This now includes support for SQL stored procedures and functions.