LMDB

Free plan LinuxMacSelf-hostedWebWindows

What LMDB is

LMDB is a free embedded key-value data store developed for the OpenLDAP Project. Memory-mapped files provide disk persistence while delivering read performance comparable to an in-memory database, with zero-copy lookup and iteration through the operating-system buffer cache. The object code is about 32KB, and sorted keys make range lookups straightforward. LMDB provides ACID transactions with MVCC, reader and writer transactions, and serialized writes without deadlocks. Readers do not block writers, writers do not block readers, and multiple processes can open one environment on a host. Multiple sub-databases can share transactions. It needs no separate process, cleanup worker, compaction, application cache, logs, or crash-recovery procedure. Utilities include mdb_stat and mdb_copy, with API documentation. LMDB supports Windows and POSIX systems such as Linux and macOS, plus languages including C, C++, Perl, Python, and PHP. Symas describes the OpenLDAP license as basically BSD-style.

Who it suits

It suits developers needing a compact, embedded key-value store on Windows, Linux, macOS, or other POSIX systems. Its transaction and concurrency model fits applications requiring persistent local data without a separate database service.

What it does well

Free embedded key-value database
About 32KB of object code
ACID transactions with MVCC
Readers and writers do not block each other
Requires no external process or crash-recovery procedure

What to know first

No data synchronization
Uses a key-value, NoSQL query model
Encryption is listed but implementation details are not provided
Professional support is fixed-price

Limits

The free plan covers LMDB itself. Source-level Gold and Enterprise support are separate fixed-price offerings, and their prices are not provided.

Plans

Plan	Billed and limits	Price
Enterprise	fixed-price · source-level support · LMDB organizations	On request
Gold	fixed-price · source-level support · LMDB organizations	On request

As symas.com lists them, read 1 Oct 2026. The maker's own page has the final word.

Getting started

Open the LMDB website
Use the development repository in the OpenLDAP Project or its GitHub clone
Build or integrate LMDB on Windows, Linux, macOS or another POSIX-compatible system
Connect through a supported language such as C, C++, Perl, Python or PHP

Verdict

LMDB emphasizes compact deployment, persistence, and concurrent transactions with minimal maintenance. It is a focused key-value store rather than a synchronized database service.

Questions

Is LMDB free?

Yes. LMDB has a free plan and is under the OpenLDAP license, which Symas describes as basically BSD-style.

Which platforms does LMDB support?

It supports Windows and POSIX-compatible systems, including Linux and macOS. It is also listed for self-hosted and web use.

What database model does LMDB use?

LMDB is an embedded key-value database with a NoSQL query interface.

Does LMDB provide encryption or synchronization?

Encryption is listed as supported. Data synchronization is listed as unsupported.

Which languages and integrations are reported?

Symas reports support for C, C++, Perl, Python, PHP and other languages, plus integrations including OpenDKIM, Heimdal Kerberos, Postfix, Cyrus SASL, MemcacheDB, SQLite3 and Riak.

Facts from LMDB's own pages

Code size: LMDB is about 32KB of object code. · symas.com, 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. · symas.com, 1 Oct 2026
Data model: Keys are always sorted, making range lookups straightforward and efficient. · symas.com, 1 Oct 2026
Headquarters: Grand Junction, Colorado, USA · symas.com, 28 Sept 2026
Integrations: Symas reports integrations with OpenDKIM, Heimdal Kerberos, Postfix, Cyrus SASL, MemcacheDB, SQLite3, and Riak. · symas.com, 1 Oct 2026
Language support: Symas reports support for C, C++, Perl, Python, PHP, and other programming languages. · symas.com, 1 Oct 2026
License: Symas states that LMDB is part of OpenLDAP and is under the OpenLDAP license, basically a BSD-style license. · symas.com, 1 Oct 2026
Maintenance: LMDB requires no external process, background cleanup, compaction, application-level cache, logs, or crash-recovery procedure. · symas.com, 1 Oct 2026
Persistence: Memory-mapped files provide read performance comparable to an in-memory database while retaining disk persistence. · symas.com, 1 Oct 2026
Purpose: LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store developed for the OpenLDAP Project. · symas.com, 1 Oct 2026
Source availability: Development occurs in the OpenLDAP Project git repository and a clone is available on GitHub. · symas.com, 1 Oct 2026
Sub-databases: LMDB supports multiple sub-databases with transactions covering all sub-databases in an environment. · symas.com, 1 Oct 2026
Support: Symas offers fixed-price Gold or Enterprise source-level support and porting or professional services for LMDB users. · symas.com, 1 Oct 2026
Transactions: LMDB provides full ACID semantics with MVCC, reader/writer transactions, and deadlock-free serialized writes. · symas.com, 1 Oct 2026
Utilities: LMDB includes mdb_stat for database status, mdb_copy for complete backups, and complete API documentation. · symas.com, 1 Oct 2026
Zero-copy access: LMDB uses memory-mapped files for zero-copy lookup and iteration and uses the operating system buffer cache. · symas.com, 1 Oct 2026

Where LMDB stands on Freedom251

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