I didn't know OpenLDAP originally ran on BDB! These days it uses its own LMDB, which has also replaced BDB in many other places.

Turns out, OpenLDAP started using BDB in 2002 and LMDB wasn't ready until 2011. In the middle of the NoSQL boom! :-)

https://en.wikipedia.org/wiki/OpenLDAP
https://en.wikipedia.org/wiki/Lightning_Memory-Mapped_Database