Overall

Brief

libmdbx is an extremely fast, compact, powerful, embedded, transactional key-value database, with Apache 2.0 license. libmdbx has a specific set of properties and capabilities, focused on creating unique lightweight solutions.

1. Allows a swarm of multi-threaded processes to ACIDly read and update several key-value maps and multimaps in a locally-shared database.
2. Provides extraordinary performance, minimal overhead through Memory-Mapping and Olog(N) operations costs by virtue of B+ tree.
3. Requires no maintenance and no crash recovery since it doesn't use WAL, but that might be a caveat for write-intensive workloads with durability requirements.
4. Enforces serializability for writers just by single mutex and affords wait-free for parallel readers without atomic/interlocked operations, while writing and reading transactions do not block each other.
5. Guarantee data integrity after crash unless this was explicitly neglected in favour of write performance.
6. Supports Linux, Windows, MacOS, Android, iOS, FreeBSD, DragonFly, Solaris, OpenSolaris, OpenIndiana, NetBSD, OpenBSD and other systems compliant with POSIX.1-2008.
7. Compact and friendly for fully embedding. Only ≈25KLOC of C11, ≈64K x86 binary code of core, no internal threads neither server process(es), but implements a simplified variant of the Berkeley DB and dbm API.

The source code is availale on Gitflic. Donations are welcome to ETH 0xD104d8f8B2dC312aaD74899F83EBf3EEBDC1EA3A. Всё будет хорошо!

Questions, feedback and suggestions are welcome to the Telegram' group (archive 1, 2, 3, 4, 5, 6, 7). See the ChangeLog for NEWS and latest updates.

Table of Contents

This manual is divided into parts, each of which is divided into several sections.

1. The Introduction
   • Characteristics
   • Improvements beyond LMDB
   • Restrictions & Caveats
   • Performance comparison
2. Usage
   • Building & Embedding
   • Getting started
   • Bindings
3. The C/C++ API manual:
   • The C API reference
   • Quick reference for Insert/Update/Delete operations
   • The mdbx.h header file reference
   • The C++ API reference
   • The mdbx.h++ header file reference

Please do not hesitate to point out errors in the documentation, including creating merge-request with corrections and improvements.

---

MithrilDB and Future

The next version is under non-public development from scratch and will be released as MithrilDB and libmithrildb for libraries & packages. Admittedly mythical Mithril is resembling silver but being stronger and lighter than steel. Therefore MithrilDB is a rightly relevant name.

MithrilDB is radically different from libmdbx by the new database format and API based on C++20. The goal of this revolution is to provide a clearer and robust API, add more features and new valuable properties of the database. All fundamental architectural problems of libmdbx/LMDB have been solved there, but now the active development has been suspended for top-three reasons:

1. For now libmdbx «mostly» enough for all our products, and I’m busy in development of replication for scalability.
2. Waiting for fresh Elbrus CPU of e2k architecture, especially with hardware acceleration of Streebog and Kuznyechik, which are required for Merkle tree, etc.
3. The expectation of needs and opportunities due to the wide use of NVDIMM (aka persistent memory), modern NVMe and Ангара.

However, MithrilDB will not be available for countries unfriendly to Russia (i.e. acceded the sanctions, devil adepts and/or NATO). But it is not yet known whether such restriction will be implemented only through a license and support, either the source code will not be open at all. Basically I am not inclined to allow my work to contribute to the profit that goes to weapons that kill my relatives and friends. NO OPTIONS.

Nonetheless, I try not to make any promises regarding MithrilDB until release.

Contrary to MithrilDB, libmdbx will forever free and open source. Moreover with high-quality support whenever possible. Tu deviens responsable pour toujours de ce que tu as apprivois. So I will continue to comply with the original open license and the principles of constructive cooperation, in spite of outright Github sabotage and sanctions. I will also try to keep (not drop) Windows support, despite it is an unused obsolete technology for us.

History

Historically, libmdbx is a deeply revised and extended descendant of the Lightning Memory-Mapped Database. At first the development was carried out within the ReOpenLDAP project. About a year later libmdbx was separated into a standalone project, which was presented at Highload++ 2015 conference.

Since 2017 libmdbx is used in Fast Positive Tables, and until 2025 development was funded by Positive Technologies. Since 2020 libmdbx is used in Ethereum: Erigon, Akula, Silkworm, Reth, etc.

On 2022-04-15 the Github administration, without any warning nor explanation, deleted libmdbx along with a lot of other projects, simultaneously blocking access for many developers. Therefore on 2022-04-21 I have migrated to a reliable trusted infrastructure. The origin for now is at GitFlic with backup at ABF by ROSA Лаб. For the same reason Github is blacklisted forever.

Since May 2024 and version 0.13 libmdbx was re-licensed under Apache-2.0 license. Please refer to the COPYRIGHT file for license change explanations.

Acknowledgments

Howard Chu hyc@o.nosp@m.penl.nosp@m.dap.o.nosp@m.rg and Hallvard Furuseth hallv.nosp@m.ard@.nosp@m.openl.nosp@m.dap..nosp@m.org are the authors of LMDB, from which libmdbx was forked in 2015.

Martin Hedenfalk marti.nosp@m.n@bz.nosp@m.ero.s.nosp@m.e is the author of btree.c code, which was used to begin development of LMDB.

License

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