-btree2q.c Single Threaded/MultiProcess with latching supplied by advisory file locking. Works with network file systems.
-threads2h.c Multi-Threaded/Multi-Process with latching implemented with test & set locks in the btree pages.
-threads2i.c Multi-Threaded/Multi-Process with latching implemented with test & set locks in the btree pages with Linux futex system calls for contention.
+btree2s.c Single Threaded/MultiProcess version that removes keys all the way back to an original empty btree, placing removed nodes on a free list. Operates under either memory mapping or file I/O. Recommended btrees hosted on network file systems.