The Lightning Memory-Mapped Database (LMDB) is a high-performance transactional database. Unlike more complex relational databases, LMDB handles only key-value pairs (stored as arbitrary byte arrays) and relies on the underlying operating system for caching and locking, keeping the code small and simple. The use of ‘zero-copy’ memory-mapped files combines the persistence of classic disk-based databases with high read performance that scales linearly over multiple cores. The size of each database is limited only by the size of the virtual address space — not physical RAM.