Symas Lightning Memory-Mapped Database (LMDB)
This page contains technical information about Symas's LMDB database library. LMDB is an ultra-fast, ultra-compact key-value embedded data store developed by Symas for the OpenLDAP Project. It uses memory-mapped files, so it has the read performance of a pure in-memory database while still offering the persistence of standard disk-based databases, and is only limited to the size of the virtual address space, (it is not limited to the size of physical RAM).
LMDB is a tiny database with some great capabilities:
- Ordered-map interface (keys are always sorted, supports range lookups)
- Fully transactional, full ACID semantics with MVCC.
- Reader/writer transactions: readers don't block writers and writers don't block readers. Writers are fully serialized, so writes are always deadlock-free.
- Read transactions are extremely cheap, and can be performed using no mallocs or any other blocking calls.
- Supports multi-thread and multi-process concurrency, environments may be opened by multiple processes on the same host.
- Multiple sub-databases may be created with transactions covering all sub-databases.
- Memory-mapped, allowing for zero-copy lookup and iteration.
- Maintenance-free, no external process or background cleanup/compaction required.
- No application-level caching. LMDB fully exploits the operating system's buffer cache.
- 32KB of object code and 6KLOC of C.
- Licensed under the OpenLDAP Public License
- It is a read-optimized design and performs reads several times faster than other DB engines, several orders of magnitude faster in many cases. It is not a write-optimized design; for heavy random write workloads other DB designs may be more suitable.
http://symas.com/mdb/#features <--- Vergleich mit LevelDB (Bitcoin-Datenbank), LMDB eindeutiger Sieger
