(From official site)
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.
A quick comparison of popular embedded key/value stores.
| Feature | LMDB | BDB | LevelDB | Kyoto TreeDB |
|---|---|---|---|---|
| ACID Transactions | x | x | ||
| Nested Transactions | x | x | ||
| Multiple Namespaces | x | x | ||
| Sorted Keys | x | x | x | x |
| Sorted Duplicate Keys | x | x | ||
| Multi-thread concurrency | x | x | x | x |
| Multi-process concurrency | x | x | ||
| No cache tuning: zero-config | x | |||
| Instantaneous crash recovery | x | |||
| Zero-copy reads | x | |||
| Zero-copy writes | x | |||
| Atomic hot backup | x |