File overall.md
Go to the documentation of this file
\mainpage Overall
\section brief Brief
<!-- section-begin overview -->
_libmdbx_ is an extremely fast, compact, powerful, embedded, transactional [key-value database](https://en.wikipedia.org/wiki/Key-value_database), with [Apache 2.0 license](https://sourcecraft.dev/dqdkfa/libmdbx/blob?file=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 [ACID](https://en.wikipedia.org/wiki/ACID)ly read and update** several key-value [maps](https://en.wikipedia.org/wiki/Associative_array) and [multimaps](https://en.wikipedia.org/wiki/Multimap) in a locally-shared database.
2. Provides **extraordinary performance**, minimal overhead through [Memory-Mapping](https://en.wikipedia.org/wiki/Memory-mapped_file) and `O(log N)` operation costs by virtue of [B+tree](https://en.wikipedia.org/wiki/B%2B_tree).
3. Requires **no maintenance and no crash recovery** since it doesn't use [WAL](https://en.wikipedia.org/wiki/Write-ahead_logging), but that might be a caveat for write-intensive workloads with durability requirements.
4. Enforces [serializability](https://en.wikipedia.org/wiki/Serializability) for writers through a single [mutex](https://en.wikipedia.org/wiki/Mutual_exclusion) and affords [wait-free](https://en.wikipedia.org/wiki/Non-blocking_algorithm#Wait-freedom) for parallel readers without atomic/interlocked operations, while **writing and reading transactions do not block each other**.
5. **Guarantees data integrity** after crash unless this was explicitly neglected in favour of write performance.
6. Supports Linux, Windows, MacOS, Harmony, Android, iOS, FreeBSD, DragonFly BSD, Solaris, OpenSolaris, OpenIndiana, NetBSD, OpenBSD and other systems compliant with **POSIX.1-2008**.
7. **Compact and friendly for full embedding**. Just a few flat source code files. Here no internal threads nor server process(es), but implements the core of the [Berkeley DB](https://en.wikipedia.org/wiki/Berkeley_DB) API with many powerful extensions.
<!-- section-end -->
The source code is available on [SourceCraft](https://sourcecraft.dev/dqdkfa/libmdbx) and mirror on [GitHub](https://github.com/Mithril-mine/libmdbx).
Donations are welcome to ETH `0xD104d8f8B2dC312aaD74899F83EBf3EEBDC1EA3A`,
BTC `bc1qzvl9uegf2ea6cwlytnanrscyv8snwsvrc0xfsu`, SOL `FTCTgbHajoLVZGr8aEFWMzx3NDMyS5wXJgfeMTmJznRi`.
Please use the `stable` branch or the latest release for production environment through staging, but the `master` branch for development a derivative projects.
Всё будет хорошо!
> Questions, feedback and suggestions are welcome to the [Telegram' group](https://t.me/libmdbx), а также [Чат в МАКС](https://max.ru/join/dKckvyuARxp1vRK-wnPur8zYCEkbR3OUOmpPWkWxp78) для разработчиков и пользователей из России.
> See the [ChangeLog](https://sourcecraft.dev/dqdkfa/libmdbx/browse/ChangeLog.md) for `NEWS` and latest updates.
\section toc Table of Contents
This manual is divided into parts,
each of which is divided into several sections.
1. The \ref intro
- \ref characteristics
- \ref improvements
- \ref restrictions
2. \ref usage
- \ref getting
- \ref starting
- \ref bindings
3. The `C/C++` API manual:
- The \ref c_api reference
- \ref c_crud_hints "Quick reference for Insert/Update/Delete operations"
- The \ref mdbx.h header file reference
- The \ref cxx_api reference
- The \ref mdbx.h++ header file reference
Please do not hesitate to point out errors in the documentation,
including creating [pull-request](https://sourcecraft.dev/dqdkfa/libmdbx/pr) with corrections and improvements.
---
\section MithrilDB MithrilDB and Future
<!-- section-begin mithril -->
The next version is under non-public development and will be released as **MithrilDB** and `libmithrildb` for libraries & packages. Admittedly mythical [Mithril](https://en.wikipedia.org/wiki/Mithril) resembles silver, but is stronger and lighter than steel. Therefore _MithrilDB_ is an aptly relevant name.
_MithrilDB_ differs radically from _libmdbx_ in 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_ is mostly enough and I am busy with scalability.
2. Waiting for fresh [Elbrus CPU](https://wiki.elbrus.ru/) of [e2k architecture](https://en.wikipedia.org/wiki/Elbrus_2000), especially with hardware acceleration of [Streebog](https://en.wikipedia.org/wiki/Streebog) and [Kuznyechik](https://en.wikipedia.org/wiki/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](https://ru.wikipedia.org/wiki/Ангара_(интерконнект)).
However, _MithrilDB_ may not be available in jurisdictions that have imposed sanctions on Russia: I do not want my work to serve, even indirectly, purposes that I cannot accept. Whether this restriction will be implemented through licensing and support terms, or by keeping the source closed, is not yet decided. My position here is simple and firm — I will not allow my work to contribute to weapons that are used against people I care about.
Nonetheless, I try not to make any promises regarding _MithrilDB_ until release.
Contrary to _MithrilDB_, _libmdbx_ will forever remain free and open source. Moreover with high-quality support whenever possible. Tu deviens responsable pour toujours de ce que tu as apprivoisé. Regardless of the earlier GitHub incident and the current sanctions, _libmdbx_ will continue to comply with the original open license and the principles of constructive cooperation. I will also keep supporting Windows, even though it is no longer a technology we use ourselves.
<!-- section-end -->
<!-- section-begin history -->
# History
Historically, _libmdbx_ is a deeply revised and extended descendant of the [Lightning Memory-Mapped Database](https://en.wikipedia.org/wiki/Lightning_Memory-Mapped_Database). At first the development was carried out within the [ReOpenLDAP](https://sourcecraft.dev/dqdkfa/reopenldap) project. About a year later _libmdbx_ was separated into a standalone project, which was [presented at Highload++ 2015 conference](http://www.highload.ru/2015/abstracts/1831.html).
Since 2017 _libmdbx_ is used in [Fast Positive Tables](https://sourcecraft.dev/dqdkfa/libfpta), and until 2025 development was funded by [Positive Technologies](https://www.ptsecurity.com). Since 2020 _libmdbx_ is used in Ethereum: [Erigon](https://github.com/erigontech/erigon), [Akula](https://github.com/akula-bft/akula), [Silkworm](https://github.com/erigontech/silkworm), [Reth](https://github.com/paradigmxyz/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 [SourceCraft](https://sourcecraft.dev/dqdkfa/libmdbx) and ~~GitHub~~ is blacklisted forever to play this role.
Since May 2024 and version 0.13 _libmdbx_ was re-licensed under Apache-2.0 license. Please refer to the [`COPYRIGHT` file](https://sourcecraft.dev/dqdkfa/libmdbx/blob/raw?file=COPYRIGHT) for license change explanation.
## Acknowledgments
Howard Chu <hyc@openldap.org> and Hallvard Furuseth <hallvard@openldap.org> are the authors of _LMDB_, from which _libmdbx_ was forked in 2015.
Martin Hedenfalk <martin@bzero.se> is the author of `btree.c` code, which was used to begin development of _LMDB_.
<!-- section-end -->
License
=======
Apache License
Version 2.0, January 2004
http://www.apache.org/licenses/
TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
1. Definitions.
"License" shall mean the terms and conditions for use, reproduction,
and distribution as defined by Sections 1 through 9 of this document.
"Licensor" shall mean the copyright owner or entity authorized by
the copyright owner that is granting the License.
"Legal Entity" shall mean the union of the acting entity and all
other entities that control, are controlled by, or are under common
control with that entity. For the purposes of this definition,
"control" means (i) the power, direct or indirect, to cause the
direction or management of such entity, whether by contract or
otherwise, or (ii) ownership of fifty percent (50%) or more of the
outstanding shares, or (iii) beneficial ownership of such entity.
"You" (or "Your") shall mean an individual or Legal Entity
exercising permissions granted by this License.
"Source" form shall mean the preferred form for making modifications,
including but not limited to software source code, documentation
source, and configuration files.
"Object" form shall mean any form resulting from mechanical
transformation or translation of a Source form, including but
not limited to compiled object code, generated documentation,
and conversions to other media types.
"Work" shall mean the work of authorship, whether in Source or
Object form, made available under the License, as indicated by a
copyright notice that is included in or attached to the work
(an example is provided in the Appendix below).
"Derivative Works" shall mean any work, whether in Source or Object
form, that is based on (or derived from) the Work and for which the
editorial revisions, annotations, elaborations, or other modifications
represent, as a whole, an original work of authorship. For the purposes
of this License, Derivative Works shall not include works that remain
separable from, or merely link (or bind by name) to the interfaces of,
the Work and Derivative Works thereof.
"Contribution" shall mean any work of authorship, including
the original version of the Work and any modifications or additions
to that Work or Derivative Works thereof, that is intentionally
submitted to Licensor for inclusion in the Work by the copyright owner
or by an individual or Legal Entity authorized to submit on behalf of
the copyright owner. For the purposes of this definition, "submitted"
means any form of electronic, verbal, or written communication sent
to the Licensor or its representatives, including but not limited to
communication on electronic mailing lists, source code control systems,
and issue tracking systems that are managed by, or on behalf of, the
Licensor for the purpose of discussing and improving the Work, but
excluding communication that is conspicuously marked or otherwise
designated in writing by the copyright owner as "Not a Contribution."
"Contributor" shall mean Licensor and any individual or Legal Entity
on behalf of whom a Contribution has been received by Licensor and
subsequently incorporated within the Work.
2. Grant of Copyright License. Subject to the terms and conditions of
this License, each Contributor hereby grants to You a perpetual,
worldwide, non-exclusive, no-charge, royalty-free, irrevocable
copyright license to reproduce, prepare Derivative Works of,
publicly display, publicly perform, sublicense, and distribute the
Work and such Derivative Works in Source or Object form.
3. Grant of Patent License. Subject to the terms and conditions of
this License, each Contributor hereby grants to You a perpetual,
worldwide, non-exclusive, no-charge, royalty-free, irrevocable
(except as stated in this section) patent license to make, have made,
use, offer to sell, sell, import, and otherwise transfer the Work,
where such license applies only to those patent claims licensable
by such Contributor that are necessarily infringed by their
Contribution(s) alone or by combination of their Contribution(s)
with the Work to which such Contribution(s) was submitted. If You
institute patent litigation against any entity (including a
cross-claim or counterclaim in a lawsuit) alleging that the Work
or a Contribution incorporated within the Work constitutes direct
or contributory patent infringement, then any patent licenses
granted to You under this License for that Work shall terminate
as of the date such litigation is filed.
4. Redistribution. You may reproduce and distribute copies of the
Work or Derivative Works thereof in any medium, with or without
modifications, and in Source or Object form, provided that You
meet the following conditions:
(a) You must give any other recipients of the Work or
Derivative Works a copy of this License; and
(b) You must cause any modified files to carry prominent notices
stating that You changed the files; and
(c) You must retain, in the Source form of any Derivative Works
that You distribute, all copyright, patent, trademark, and
attribution notices from the Source form of the Work,
excluding those notices that do not pertain to any part of
the Derivative Works; and
(d) If the Work includes a "NOTICE" text file as part of its
distribution, then any Derivative Works that You distribute must
include a readable copy of the attribution notices contained
within such NOTICE file, excluding those notices that do not
pertain to any part of the Derivative Works, in at least one
of the following places: within a NOTICE text file distributed
as part of the Derivative Works; within the Source form or
documentation, if provided along with the Derivative Works; or,
within a display generated by the Derivative Works, if and
wherever such third-party notices normally appear. The contents
of the NOTICE file are for informational purposes only and
do not modify the License. You may add Your own attribution
notices within Derivative Works that You distribute, alongside
or as an addendum to the NOTICE text from the Work, provided
that such additional attribution notices cannot be construed
as modifying the License.
You may add Your own copyright statement to Your modifications and
may provide additional or different license terms and conditions
for use, reproduction, or distribution of Your modifications, or
for any such Derivative Works as a whole, provided Your use,
reproduction, and distribution of the Work otherwise complies with
the conditions stated in this License.
5. Submission of Contributions. Unless You explicitly state otherwise,
any Contribution intentionally submitted for inclusion in the Work
by You to the Licensor shall be under the terms and conditions of
this License, without any additional terms or conditions.
Notwithstanding the above, nothing herein shall supersede or modify
the terms of any separate license agreement you may have executed
with Licensor regarding such Contributions.
6. Trademarks. This License does not grant permission to use the trade
names, trademarks, service marks, or product names of the Licensor,
except as required for reasonable and customary use in describing the
origin of the Work and reproducing the content of the NOTICE file.
7. Disclaimer of Warranty. Unless required by applicable law or
agreed to in writing, Licensor provides the Work (and each
Contributor provides its Contributions) on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
implied, including, without limitation, any warranties or conditions
of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
PARTICULAR PURPOSE. You are solely responsible for determining the
appropriateness of using or redistributing the Work and assume any
risks associated with Your exercise of permissions under this License.
8. Limitation of Liability. In no event and under no legal theory,
whether in tort (including negligence), contract, or otherwise,
unless required by applicable law (such as deliberate and grossly
negligent acts) or agreed to in writing, shall any Contributor be
liable to You for damages, including any direct, indirect, special,
incidental, or consequential damages of any character arising as a
result of this License or out of the use or inability to use the
Work (including but not limited to damages for loss of goodwill,
work stoppage, computer failure or malfunction, or any and all
other commercial damages or losses), even if such Contributor
has been advised of the possibility of such damages.
9. Accepting Warranty or Additional Liability. While redistributing
the Work or Derivative Works thereof, You may choose to offer,
and charge a fee for, acceptance of support, warranty, indemnity,
or other liability obligations and/or rights consistent with this
License. However, in accepting such obligations, You may act only
on Your own behalf and on Your sole responsibility, not on behalf
of any other Contributor, and only if You agree to indemnify,
defend, and hold each Contributor harmless for any liability
incurred by, or claims asserted against, such Contributor by reason
of your accepting any such warranty or additional liability.
END OF TERMS AND CONDITIONS