SQLIte v4 supposed to be built on top of LMDB as I remember. For some reason the project was closed, they even have note about it on the official site somewhere.
SQLite v4 was supposed to have modular, pluggable backends, of which LMDB was only the first (of hopefully many). They were also working on their own from-scratch implementation of an LSM backend, which was also abandoned.
As I recall, they decided that the mmap-related performance tricks they learned from working with LMDB could just be plugged into their own SQLite v3 Btree engine. (Indeed, recent SQLitev3 is a bit faster than when the SQLitev4 project began. But still doesn't match LMDB.)
As I recall, they decided that the mmap-related performance tricks they learned from working with LMDB could just be plugged into their own SQLite v3 Btree engine. (Indeed, recent SQLitev3 is a bit faster than when the SQLitev4 project began. But still doesn't match LMDB.)