MDBM

MDBM is an open-source embedded key-value database library that provides a persistent, disk-backed store using memory-mapped I/O. It is designed for high performance and a lightweight footprint, making it suitable for caching, session storage, and other workloads that require fast key-value access with simple durability guarantees. The library is written in C and offers a straightforward API for applications to create or open a database file, store and retrieve values by key, delete keys, and iterate over entries. Operations are designed to be fast and support concurrent access by multiple processes and threads through the same database file, with configuration options to tune memory usage, page size, and the size of the in-memory cache.

MDBM stores data in a hashed layout on disk, enabling efficient average-time lookups for key-value pairs. It uses a memory-mapped representation to reduce copying and to allow the operating system to manage paging. The API typically includes functions to open or create a database, store or update a key-value pair, fetch a value by key, delete a key, and close the database; batch and iteration helpers are often provided.

MDBM has been used in various open-source and embedded projects as a lightweight alternative to heavier database systems when simple, fast key-value storage is sufficient. It competes with other embedded stores in terms of footprint and performance, and is commonly chosen for applications requiring low-latency access to a compact on-disk store.