LMDB
LMDB is a free embedded key-value database developed for the OpenLDAP Project.
What LMDB is
LMDB is a free embedded key-value database developed for the OpenLDAP Project. It stores data in memory-mapped files, combining disk persistence with read speeds comparable to an in-memory database. The database model is NoSQL, with keys kept sorted for range lookups. LMDB provides ACID transactions through MVCC, including reader and writer transactions, serialized deadlock-free writes, and transaction coverage across multiple sub-databases. Readers and writers do not block each other, and multiple processes can open one environment on a host. Memory mapping enables zero-copy lookup and iteration while using the operating system buffer cache. The approximately 32KB object code is compact. No separate process, cleanup, compaction, application cache, logs, or crash-recovery procedure is required. LMDB supports Windows, Linux, macOS, and other POSIX systems, with encryption and language support including C, C++, Perl, Python, and PHP.
Good
- Free plan available
- Approximately 32KB of object code
- ACID transactions with MVCC
- Readers and writers do not block
- Includes backup and status utilities
Watch out
- No data synchronization
- Enterprise and Gold support prices unlisted
- Requires self-hosted deployment
Who it suits
LMDB suits developers needing a compact embedded key-value store for Windows or POSIX-compatible systems. It is also relevant when sorted keys, concurrent access, transactions, and local persistence are required.
Verdict
LMDB focuses on compact local storage, transactional consistency, and concurrent access without background database services. Its free license and broad platform support suit embedded database projects, while the lack of synchronization may matter for distributed use.
Plans and prices
From LMDB's own pricing page, checked 1 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| Enterprise | Priced on request | source-level support · LMDB organizations · fixed-price |
| Gold | Priced on request | source-level support · LMDB organizations · fixed-price |
The facts
Each one read from LMDB's own pages, with the date it was checked.
What it does
- Code size
- LMDB is about 32KB of object code.checked 1 Oct 2026
- Concurrency
- Readers do not block writers, writers do not block readers, and multiple processes can open the same environment on one host.checked 1 Oct 2026
- Data model
- Keys are always sorted, making range lookups straightforward and efficient.checked 1 Oct 2026
- Integrations
- Symas reports integrations with OpenDKIM, Heimdal Kerberos, Postfix, Cyrus SASL, MemcacheDB, SQLite3, and Riak.checked 1 Oct 2026
- Language support
- Symas reports support for C, C++, Perl, Python, PHP, and other programming languages.checked 1 Oct 2026
- License
- Symas states that LMDB is part of OpenLDAP and is under the OpenLDAP license, basically a BSD-style license.checked 1 Oct 2026
- Maintenance
- LMDB requires no external process, background cleanup, compaction, application-level cache, logs, or crash-recovery procedure.checked 1 Oct 2026
- Persistence
- Memory-mapped files provide read performance comparable to an in-memory database while retaining disk persistence.checked 1 Oct 2026
- Purpose
- LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store developed for the OpenLDAP Project.checked 1 Oct 2026
- Source availability
- Development occurs in the OpenLDAP Project git repository and a clone is available on GitHub.checked 1 Oct 2026
- Sub-databases
- LMDB supports multiple sub-databases with transactions covering all sub-databases in an environment.checked 1 Oct 2026
- Support
- Symas offers fixed-price Gold or Enterprise source-level support and porting or professional services for LMDB users.checked 1 Oct 2026
- Transactions
- LMDB provides full ACID semantics with MVCC, reader/writer transactions, and deadlock-free serialized writes.checked 1 Oct 2026
- Utilities
- LMDB includes mdb_stat for database status, mdb_copy for complete backups, and complete API documentation.checked 1 Oct 2026
- Zero-copy access
- LMDB uses memory-mapped files for zero-copy lookup and iteration and uses the operating system buffer cache.checked 1 Oct 2026
The company
- Headquarters
- Grand Junction, Colorado, USAchecked 28 Sep 2026
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