Yeah, there's a global lock for transactions. I'm not sure it's such a big loss considering you still need a lock on the log file. Adding MVCC or per-object locks would mean rewriting most of BKNR, changing major parts of how it works, and a hugely more complicated implementation. And those things have a lot of their own overhead too. OTOH then you can just throw the objects into an mmapped file, put a REPL on a socket and bingo you have a multi-user networked ACID object database. But then you might as well just use Postgresql and Postmodern.

I don't know if you've ever installed the full Kloudshare, but Will wrote the first Hold backed by bknr.datastore, so you've probably used it.