I find the Bw-tree work pretty underwhelming. It's not a transactional engine; the fact that it can operate "latch-free" is irrelevant since it must be wrapped by some higher concurrency management layer to truly be useful. The delta-update mechanism is probably more write-efficient than LMDB, which could be a point in their favor. The fact that they still rely on an application-level page cache manager is a strong negative - you can never manage the cache more accurately and more efficiently than the kernel, which gets hardware assist for free. Overall, it's an awful lot of noise being made over not much actual innovation.