Lessfs-1.5.10 adds support for hamsterdb-2.0.1. A small change in the Hamsterdb API makes the transition from the 1.x series not completely transparent. Do not use Lessfs with hamsterdb-2.0 since it comes with a nasty bug. Please use the latest hamsterdb-2.0.1.
When compared with Berkeley DB hamsterdb does not suffer from the performance degradation that comes with Berkeley DB when the databases are becoming large. Hamsterdb 2.X performance is considerably better then Berkeley DB or even Tokyocabinet. The code is however not that well tested or as much used as the others.