[pclmulqdq]

GP wrote a key-value store called LMDB that is constrained to a single writer, and often used for small databases that fit entirely in memory but need to persist to disk. There's a whole different world for more scalable databases.

[hyc_symas]

"fit entirely in memory" is not a requirement. LMDB is not a main-memory database, it is an on-disk database that uses memory mapping.