Lightning Memory-Mapped Database

LMDB's design was first discussed in a 2009 post to the OpenLDAP developer mailing list,[http://marc.info/?l=openldap-devel&m=124253456912512 back-mdb - futures]. Retrieved on 2014-10-19 in the context of exploring solutions to the cache management difficulty caused by the project's dependence on Berkeley DB. A specific goal was to replace the multiple layers of configuration and caching inherent to Berkeley DB's design with a single, automatically managed cache under the control of the host operating system.

Development subsequently began, initially as a fork of a similar implementation from the OpenBSD ldapd project.[http://www.openldap.org/pub/hyc/mdb-paper.pdf MDB: A Memory-Mapped Database and Backend for OpenLDAP]. Retrieved 2018-10-22 The first publicly available version appeared in the OpenLDAP source repository in June 2011.[https://git.openldap.org/openldap/openldap/-/commit/d620d4368a7ee17d60f2b381d4c80b22c68ba8e2 First public version of MDB source code]. Retrieved 2020-03-16

The project was known as MDB until November 2012, after which it was renamed in order to avoid conflicts with existing software.[https://git.openldap.org/openldap/openldap/-/commit/13f3bcd59c2055d53e4759b0c3356b001eca44b0 MDB renamed to LMDB]. Retrieved 2020-03-16

Internally LMDB uses B+ tree data structures. The efficiency of its design and small footprint had the unintended side-effect of providing good write performance as well. LMDB has an API similar to Berkeley DB and dbm. LMDB treats the computer's memory as a single address space, shared across multiple processes or threads using shared memory with copy-on-write semantics (known historically as a single-level store). Most former modern computing architectures had a 32-bit memory address space, imposing a hard limit of 4 GB on the size of any database that directly mapped into a single-level store. However, today's 64-bit processors now mostly implement 48-bit address spaces, giving access to 47-bit addresses or 128 TB of database size,{{cite conference | url=http://ldapcon.org/2011/downloads/chu-paper.pdf | title=MDB: A Memory-Mapped Database and Backend for OpenLDAP | last=Chu | first=Howard | conference=LDAPCon | conference-url=http://ldapcon.org/2011/ | year=2011}}. making databases using shared memory useful once again in real-world applications.

Specific noteworthy technical features of LMDB are:

• Its use of B+ tree. With an LMDB instance being in shared memory and the B+ tree block size being set to the OS page size, access to an LMDB store is extremely memory efficient.B+ tree#Implementation
• New data is written without overwriting or moving existing data. This guarantees data integrity and reliability without requiring transaction logs or cleanup services.
• The provision of a unique append-write mode (MDB_APPEND) is implemented by allowing the new record to be added directly to the end of the B+ tree. This reduces the number of reads and writes page operations, resulting in greatly-increased performance but requiring the programmer to ensure keys are already in sorted order when storing in the DB.
• Copy-on-write semantics help ensure data integrity as well as providing transactional guarantees and simultaneous access by readers without requiring any locking, even by the current writer. New memory pages required internally during data modifications are allocated through copy-on-write semantics by the underlying OS: the LMDB library itself never actually modifies older data being accessed by readers because it simply cannot do so: any shared-memory updates automatically create a completely independent copy of the memory-page being written to.
• As LMDB is memory-mapped, it can return direct pointers to memory addresses of keys and values through its API, thereby avoiding unnecessary and expensive copying of memory. This results in greatly-increased performance (especially when the values stored are extremely large), and expands the potential use cases for LMDB.
• LMDB also tracks unused memory pages, using a B+ tree to keep track of pages freed (no longer needed) during transactions. By tracking unused pages, the need for garbage collection (and a garbage collection phase that would consume CPU cycles) is completely avoided. Transactions that need new pages are first given pages from this unused free pages tree; only after these are used up will it expand into formerly unused areas of the underlying memory-mapped file. On a modern filesystem with sparse file support, this helps minimise actual disk usage.

The file format of LMDB is, unlike that of Berkeley DB, architecture-dependent. This means that a conversion must be done before moving a database from a 32-bit machine to a 64-bit machine,{{cite web |title=The LMDB file format |url=https://blog.separateconcerns.com/2016-04-03-lmdb-format.html |website=Separate Concern |accessdate=27 February 2020}} or between computers of differing endianness.{{cite web |last1=Chu |first1=Howard |title=lmdb - Is the Monero blockchain database portable between 32 and 64 bit architectures, and little/big endian architectures? |url=https://monero.stackexchange.com/a/4526 |website=Monero Stack Exchange}}

LMDB employs multiversion concurrency control (MVCC) and allows multiple threads within multiple processes to coordinate simultaneous access to a database. Readers scale linearly by design.[http://www.lmdb.tech/bench/inmem/scaling.html scaling benchmarks for LMDB][http://www.lmdb.tech/bench/inmem/scale2/ in-memory benchmark scaling for LMDB] While write transactions are globally serialized via a mutex, read-only transactions operate in parallel, including in the presence of a write transaction. They are entirely wait free except for the first read-only transaction on a thread. Each thread reading from a database gains ownership of an element in a shared memory array, which it may update to indicate when it is within a transaction. Writers scan the array to determine the oldest database version the transaction must preserve without requiring direct synchronization with active readers.

In 2011, Google published software that allowed users to generate micro-benchmarks comparing LevelDB's performance to SQLite and Kyoto Cabinet in different scenarios.{{cite web|title=LevelDB Benchmarks|url=http://leveldb.googlecode.com/svn/trunk/doc/benchmark.html|publisher=Google, Inc.|accessdate=8 August 2014|archive-url=https://web.archive.org/web/20110820001028/http://leveldb.googlecode.com/svn/trunk/doc/benchmark.html|archive-date=20 August 2011|url-status=dead}} In 2012, Symas added support for LMDB and Berkeley DB and made the updated benchmarking software publicly available.{{cite web|last1=Chu |first1=Howard |title=Database Microbenchmarks |url=http://www.lmdb.tech/bench/microbench/ |publisher=Symas Corp. |accessdate=8 August 2014 |url-status=live |archive-url=https://web.archive.org/web/20140809204443/http://symas.com/mdb/microbench/ |archive-date= 9 August 2014 }} The resulting benchmarks showed that LMDB outperformed all other databases in read and batch write operations. SQLite with LMDB excelled in write operations, and particularly so on synchronous/transactional writes.

The benchmarks showed the underlying filesystem as having a big influence on performance. JFS with an external journal performs well, especially compared to other modern systems like Btrfs and ZFS.{{cite web | url=http://lmdb.tech/bench/microbench/|title=MDB Microbenchmarks|publisher=Symas Corp.}}, 2012-09[http://lmdb.tech/bench/microbench/july/ Database Microbenchmarks], Symas Corp., 2012-07.

Zimbra has tested back-mdb vs back-hdb performance in OpenLDAP, with LMDB clearly outperforming the BDB based back-hdb.{{cite web | url=http://wiki.zimbra.com/wiki/OpenLDAP_MDB_vs_HDB_performance|title=OpenLDAP MDB vs HDB performance|publisher=Zimbra, Inc.}} Many other OpenLDAP users have observed similar benefits.{{cite web|url=https://mishikal.wordpress.com/2013/05/16/openldap-a-comparison-of-back-mdb-and-back-hdb-performance/|title=OpenLDAP: A comparison of back-mdb and back-hdb performance|date=16 May 2013|accessdate=8 May 2017}}

Since the initial benchmarking work done in 2012, multiple follow-on tests have been conducted with additional database engines for both in-memory{{cite web|last1=Chu|first1=Howard|title=In-Memory Microbenchmark|url=http://www.lmdb.tech/bench/inmem/|publisher=Symas Corp.|access-date=2014-12-06|archive-url=https://web.archive.org/web/20141209233002/http://symas.com/mdb/inmem/|archive-date=2014-12-09|url-status=live}} and on-disk{{cite web|last1=Chu|first1=Howard|title=On-Disk Microbenchmark|url=http://www.lmdb.tech/bench/ondisk/|publisher=Symas Corp.|access-date=2014-12-06|archive-url=https://web.archive.org/web/20141209233807/http://symas.com/mdb/ondisk/|archive-date=2014-12-09|url-status=live}} workloads characterizing the performance across multiple CPUs and record sizes. These tests show that LMDB performance is unmatched on all in-memory workloads and excels in all disk-bound read workloads and disk-bound write workloads using large record sizes. The benchmark driver code was subsequently published on GitHub{{cite web|title=Benchmark Drivers|website=GitHub |url=https://github.com/hyc/leveldb/tree/benches/doc/bench}} and further expanded in database coverage.

LMDB was designed to resist data loss in the face of system and application crashes. Its copy-on-write approach never overwrites currently-in-use data. Avoiding overwrites means the structure on disk/storage is always valid, so application or system crashes can never leave the database in a corrupted state. In its default mode, at worst, a crash can lose data from the last not-yet-committed write transaction. Even with all asynchronous modes enabled, it is only an OS catastrophic failure or hardware power-loss{{cite web | url=https://bugs.openldap.org/show_bug.cgi?id=7668|title=LMDB Corruption detection}} event rather than merely an application crash that could potentially result in any data corruption.

Two academic papers from the USENIX OSDI Symposium{{cite web | url=https://www.usenix.org/conference/osdi14|title=OSDI 2014|date=2013-02-08}} covered failure modes of DB engines (including LMDB) under a sudden power loss or system crash.{{cite book | url=https://www.usenix.org/conference/osdi14/technical-sessions/presentation/pillai|title=OSDI 2014, All File Systems Are Not Created Equal: On the Complexity of Crafting Crash-Consistent Applications|pages=433–448|isbn=9781931971164|year=2014|last1=Langston|first1=Mark C.|last2=Skelly|first2=Hal}}{{cite book | url=https://www.usenix.org/conference/osdi14/technical-sessions/presentation/zheng_mai|title=OSDI 2014, Torturing Databases for Fun and Profit|pages=449–464|isbn=9781931971164|year=2014|last1=Langston|first1=Mark C.|last2=Skelly|first2=Hal}} The paper from Pillai et al., did not find any failure in LMDB that would occur in the real-world file systems considered; the single failure identified by the study in LMDB only relates to hypothetical file systems.{{cite web | url=http://www.openldap.org/lists/openldap-devel/201410/msg00004.html|title=Archive of discussion regarding the Usenix 2014 pillai paper}} The Mai Zheng et al. paper claims to point out failures in LMDB, but the conclusion depends on whether fsync or fdatasync is utilised. Using fsync ameliorates the problem. The selection of fsync over fdatasync is a compile-time switch that is not the default behavior in current Linux builds of LMDB but is the default on macOS, *BSD, Android, and Windows. Default Linux builds of LMDB are, therefore, the only ones vulnerable to the problem discovered by the zhengmai researchers however, LMDB may simply be rebuilt by Linux users to utilise fsync instead.{{cite web | url=http://www.openldap.org/lists/openldap-devel/201410/msg00008.html|title=LMDB Crash consistency discussion}}

When provided with a corrupt database, such as one produced by fuzzing, LMDB may crash. LMDB's author considers the case unlikely to be concerning but has produced a partial fix in a separate branch.{{cite web |last1=Debroux |first1=Lionel |title=oss-security - Fun with DBM-type databases... |url=https://www.openwall.com/lists/oss-security/2018/06/17/1 |website=openwall.com |date=16 Jun 2018}}

In June 2013, Oracle changed the license of Berkeley DB (a related project) from the Sleepycat license to the Affero General Public License,{{cite web | url=https://oss.oracle.com/pipermail/bdb/2013-June/000056.html|title=Berkeley DB Release Announcement|date=11 June 2013 |publisher=Oracle Corporation |quote=Starting with the 6.0 / 12c releases, all Berkeley DB products are licensed under the GNU AFFERO GENERAL PUBLIC LICENSE (AGPL), version 3. This license is published by the Free Software Foundation (FSF) (1) and approved by the Open Source Initiative (2). Please review the terms of the license to ensure compliance before upgrading to the 12c release. Previous releases of Berkeley DB software will continue to be distributed under the Sleepycat license.}} thus restricting its use in a wide variety of applications. This caused the Debian project to exclude the library from 6.0 onwards. It was also criticized that this license is not friendly to commercial redistributors. The discussion was sparked over whether the same licensing change could happen to LMDB. Author Howard Chu clarified that LMDB is part of the OpenLDAP project, which had its BSD-style license before he joined, and it will stay like it. No copyright is transferred to anybody by checking in, which would make a similar move like Oracle's impossible.{{cite mailing list | url=http://lists.debian.org/debian-devel/2013/07/msg00031.html |title=Berkeley DB 6.0 license change to AGPLv3 |date=July 2, 2013 |mailing-list=debian-devel |publisher=Debian |author=Ondřej Surý}}{{cite news |url=http://www.infoworld.com/d/open-source-software/oracle-switches-berkeley-db-license-222097 |title=Oracle switches Berkeley DB license |author=Simon Phipps |date=July 5, 2013 |publisher=InfoWorld}}{{cite web | url=http://developers.slashdot.org/story/13/07/05/1647215/oracle-quietly-switches-berkeleydb-to-agpl|title=Oracle Quietly Switches BerkeleyDB to AGPL|date=5 July 2013 |publisher=Slashdot}}{{cite web |url=http://programmers-in-ua.blogspot.com/2013/07/oracle-berkeley-db.html |title=Oracle меняет лицензию Berkeley DB |publisher=Blogspot |website=Programmers in Ukraine |date=July 22, 2013 |language=ru |trans-title=Oracle Berkeley DB license changes}}{{cite web | url=http://www.lemondeinformatique.fr/actualites/lire-oracle-passe-berkeley-db-sous-licence-gnu-agpl-54287.html|title=Oracle passe Berkeley DB sous licence GNU AGPL |language=fr |trans-title=Oracle Berkeley DB passes under GNU AGPL |date=July 8, 2013 |author= Jean Elyan |publisher=Le Monde Informatique}}{{cite web | url=http://www.abclinuxu.cz/zpravicky/berkeley-db-6.0-vydana-pod-licenci-agplv3 |title=Berkeley DB 6.0 vydána pod licencí AGPLv3 |language=cs |trans-title=Berkeley DB 6.0 is released under the GPLv3 license |date=July 2, 2013 |author=Ondřej Surý |publisher=Abclinuxu}}{{cite web | url=https://lwn.net/Articles/557820/ |title=Debian, Berkeley DB, and AGPLv3 |author=Nathan Willis |date=July 10, 2013 |publisher=LWN.net}}{{cite mailing list | url=https://lists.debian.org/debian-devel/2013/07/msg00047.html |title=Berkeley DB 6.0 license change to AGPLv3 |date=July 2, 2013 |mailing-list=debian-devel |publisher=Debian |author=Dan Shearer}}{{cite mailing list | url=https://lists.debian.org/debian-devel/2013/07/msg00067.html |title=Berkeley DB 6.0 license change to AGPLv3 |date=July 2, 2013 |mailing-list=debian-devel |publisher=Debian |author=Howard Chu}}

The Berkeley DB license issue has caused major Linux distributions such as Debian to completely phase out their use of Berkeley DB, with a preference for LMDB.{{cite mailing list | url=https://lists.debian.org/debian-devel/2014/06/msg00338.html | title=New project goal: Get rid of Berkeley DB (post jessie) | mailing-list=debian-devel | date=June 19, 2014 | author=Ondřej Surý |publisher=Debian}}

There are wrappers for several programming languages, such as C++,[https://github.com/bendiken/lmdbxx LMDB C++11 wrapper], 2015-04[https://code.google.com/p/libglim/source/browse/trunk/mdb.hpp LMDB C++ wrapper], 2012-11. Java,[https://github.com/lmdbjava/lmdbjava LmdbJava], 2019-04 Python,[https://github.com/dw/py-lmdb/ LMDB Python wrapper], 2013-02[http://lmdb.readthedocs.org py-lmdb]. Retrieved on 2014-10-20. Lua,[https://github.com/shmul/lightningdbm LMDB Lua wrapper], 2013-04. Rust,[https://github.com/meilisearch/heed typed LMDB Rust wrapper], 2023-01[https://github.com/mozilla/rkv high-level Rust wrapper], 2022-12 Go,[https://github.com/bmatsuo/lmdb-go LMDB Go wrapper], 2013-03 Ruby,[https://github.com/minad/lmdb LMDB Ruby wrapper], 2013-02 Objective C,[https://github.com/rbartolome/LMDBKit LMDB Objective-C wrapper], 2013-04 Javascript,[https://github.com/Venemo/node-lmdb LMDB Node.js wrapper], 2013-05 C#,[https://github.com/ilyalukyanov/Lightning.NET LMDB .Net wrapper], 2013-06 Perl,[http://search.cpan.org/dist/LMDB_File/ LMDB Perl wrapper], 2013-08 PHP,[https://github.com/mpremus/lmdb-php LMDB PHP wrapper], 2015-04 Tcl[https://core.tcl.tk/jenglish/gutter/packages/lmdb.html tcl-lmdb], 2015-11 and Common Lisp.[http://eudoxia.me/article/lmdb-from-common-lisp Using LMDB from Common Lisp], 2016-04 A complete list of wrappers may be found on the main web site.{{cite web|url=https://www.symas.com/symas-lmdb-tech-info|title=Symas LMDB Tech Info}}

Howard Chu ported SQLite 3.7.7.1 to use LMDB instead of its original B-tree code, calling the result SQLightning.{{cite web|url=http://gitorious.org/mdb/sqlightning|title=gitorious.org Git - mdb:sqlightning.git/summary|website=gitorious.org|accessdate=8 May 2017|archive-url=https://web.archive.org/web/20130809145553/http://gitorious.org/mdb/sqlightning|archive-date=9 August 2013|url-status=live}} One cited insert test of 1000 records was 20 times faster (than the original SQLite with its B-Tree implementation).[http://pastebin.com/B5SfEieL SQLightning tests]. LMDB is available as a backing store for other open source projects including Cyrus SASL,{{cite web|url=http://cyrusimap.web.cmu.edu/|title=Cyrus IMAP — Cyrus IMAP 3.0.1 (stable) documentation|website=cyrusimap.web.cmu.edu|accessdate=8 May 2017|url-status=dead|archive-url=https://web.archive.org/web/20170430023937/http://cyrusimap.web.cmu.edu/|archive-date=30 April 2017}} Heimdal Kerberos,{{cite web|url=http://h5l.org/|title=Heimdal|website=h5l.org|accessdate=8 May 2017}} and OpenDKIM.{{cite web|url=http://www.opendkim.org/|title=OpenDKIM|website=www.opendkim.org|accessdate=8 May 2017}} It is also available in some other NoSQL projects like MemcacheDB {{cite web|url=https://gitorious.org/mdb/memcachedb|title=gitorious.org Git - mdb:memcachedb.git/summary|website=gitorious.org|accessdate=8 May 2017}} and Mapkeeper.{{cite web|url=https://github.com/m1ch1/mapkeeper/|title=GitHub - m1ch1/mapkeeper: Thrift based key-value store with various storage backends, including MySQL, Berkeley DB, and LevelDB.|website=github.com|url-status=dead|archive-url=https://web.archive.org/web/20160209024233/https://github.com/m1ch1/mapkeeper/|archive-date=9 February 2016}} LMDB was used to make the in-memory store Redis persist data on disk. The existing back-end in Redis showed pathological behaviour in rare cases, and a replacement was sought. The baroque API of LMDB was criticized though, forcing a lot of coding to get simple things done. However, its performance and reliability during testing was considerably better than the alternative back-end stores that were tried.{{cite web|url=http://www.anchor.com.au/blog/2013/05/second-strike-with-lightning/|title=Second Strike With Lightning|publisher=Anchor|date=2013-05-09}}

An independent third-party software developer utilised the Python bindings to LMDB{{cite web | url=http://lmdb.readthedocs.org|title=Python bindings to LMDB}} in a high-performance environment and published, on the technology news site Slashdot, how the system managed to successfully sustain 200,000 simultaneous read, write and delete operations per second (a total of 600,000 database operations per second).{{cite web | url=http://developers.slashdot.org/story/14/10/17/1547222/python-lmdb-in-a-high-performance-environment|title=Python-LMDB in a high-performance environment on Slashdot|date=17 October 2014 }}{{cite web | url=http://lkcl.net/reports/python.lmdb.html|title=Open letter to Howard Chu and David Wilson regarding Python-LMDB}}

An up-to-date list of applications using LMDB is maintained on the main web site.{{cite web|url=https://www.symas.com/symas-lmdb-tech-info|title=List of projects using LMDB}}

Many popular free software projects distribute or include support for LMDB, often as the primary or sole storage mechanism.

• The Debian,[https://packages.debian.org/liblmdb0 liblmdb0 in Debian]. Retrieved 2014-10-20. Ubuntu,{{cite web|url=https://packages.ubuntu.com/lmdb-utils|title=Ubuntu – Package Search Results -- lmdb-utils|first=Rhonda|last=D'Vine|website=packages.ubuntu.com|accessdate=2 Jan 2018}} Fedora,[http://rpm.pbone.net/index.php3/stat/4/idpl/26914801/dir/fedora_20/com/lmdb-0.9.13-1.fc20.i686.rpm.html LMDB in Fedora 20]. Retrieved 2014-10-20. and OpenSuSE[http://rpm.pbone.net/index.php3/stat/4/idpl/27477943/dir/opensuse/com/lmdb-0.9.11-4.2.2.x86_64.rpm.html lmdb in OpenSUSE]. Retrieved 2014-10-20. operating systems.
• OpenLDAP for which LMDB was originally developed via {{mono|back-mdb}}.[http://www.openldap.org/doc/admin24/backends.html#LMDB OpenLDAP back-mdb]. Retrieved 2014-10-20
• Postfix via the {{mono|lmdb_table}} adapter.[http://www.postfix.org/lmdb_table.5.html Postfix lmdb_table(5)]. Retrieved 2014-10-20
• PowerDNS, a DNS server.
• CFEngine uses LMDB by default since version of 3.6.0.{{cite web|url=https://docs.cfengine.com/docs/3.6/guide-latest-release-whatsnew.html|title=CFEngine 3.6 Documentation - New in CFEngine|website=docs.cfengine.com|accessdate=8 May 2017}}
• Shopify use LMDB in their SkyDB system.{{cite web|url=https://groups.google.com/d/msg/skydb/CMKQSLf2WAw/zBO1X35alxcJ|title=Google Groups|website=groups.google.com|accessdate=8 May 2017}}
• Knot DNS a high performance DNS server.
• Monero an open source cryptocurrency created in April 2014 that focuses on privacy, decentralisation and scalability.
• Enduro/X middleware uses LMDB for optional XATMI Microservices (SOA) cache. For the first request the actual service is invoked; in the next request client process reads the saved result directly from LMDB.
• Samba Active Directory Domain Controller
• Nano a peer-to-peer, open source cryptocurrency created in 2015 that prioritizes fast and fee-less transactions.
• Meilisearch an open source, lightning-fast, easy-to-use, and hyper-relevant search engine.{{cite web|url=https://docs.meilisearch.com/learn/advanced/storage.html|title=Storage | Meilisearch Documentation v1.0|access-date=21 Mar 2023}}
• LMDB-IndexedDB is a JavaScript wrapper around IndexedDB to provide support for LMDB in web browsers.{{cite web|url=https://github.com/anywhichway/lmdb-indexeddb|title=LMDB-IndexedDB on GitHub|website=GitHub |access-date=2 Apr 2023}}

LMDB makes novel use of well-known computer science techniques such as copy-on-write semantics and B+ trees to provide atomicity and reliability guarantees as well as performance that can be hard to accept, given the library's relative simplicity and that no other similar key-value store database offers the same guarantees or overall performance, even though the authors explicitly state in presentations that LMDB is read-optimised not write-optimised. Additionally, as LMDB was primarily developed for use in OpenLDAP, its developers are focused mainly on the development and maintenance of OpenLDAP, not on LMDB per se. The developers limited time spent presenting the first benchmark results was therefore criticized as not stating limitations and for giving a "silver bullet impression" not adequate to address an engineers attitude{{cite web | url=http://banksco.de/p/lmdb-the-leveldb-killer.html|title=LMDB: The Leveldb Killer?}} (it has to be pointed out that the concerns raised however were later adequately addressed to the reviewer's satisfaction by the key developer behind LMDB.{{cite web | url=https://symas.com/is-lmdb-a-leveldb-killer/|title=Response to LMDB review|archive-url=https://web.archive.org/web/20201111195059/https://symas.com/is-lmdb-a-leveldb-killer/|url-status=dead |website=symas.com|archive-date=11 November 2020}})

The presentation did spark other database developers to dissect the code in-depth to understand how and why it works. Reviews run from brief {{cite web | url=http://kellabyte.com/2013/07/09/lightning-memory-mapped-database/|title=Lightning Memory-Mapped Database|archive-url=https://web.archive.org/web/20160314133119/http://kellabyte.com/2013/07/09/lightning-memory-mapped-database/|archive-date=14 March 2016}} to in-depth. Database developer Oren Eini wrote a 12-part series of articles on his analysis of LMDB, beginning July 9, 2013. The conclusion was in the lines of "impressive codebase ... dearly needs some love", mainly because of too long methods and code duplication.{{cite web | url=http://ayende.com/blog/162754/reviewing-lightning-memory-mapped-database-library-partial|title=Reviewing Lightning memory-mapped database library: Partial}} This review, conducted by a .NET developer with no former experience of C, concluded on August 22, 2013, with "beyond my issues with the code, the implementation is really quite brilliant. The way LMDB manages to pack so much functionality by not doing things is quite impressive... I learned quite a lot from the project, and it has been frustrating, annoying and fascinating experience".{{cite web | url=http://ayende.com/blog/162917/some-final-notes-about-lmdb-review|title=Some final notes about LMDB review}}

Multiple other reviews cover LMDB{{cite web|url=https://mozilla.github.io/firefox-browser-architecture/text/0015-rkv.html|title=Design Review: Key-Value Storage|website=mozilla.github.io|quote=We propose the standardization of a simple key-value storage capability, based on LMDB, that is fast, compact, multi-process-capable, and equally usable from JS, Java, Rust, Swift, and C++.}}{{cite web|url=http://sampathherga.in/lmdb/|title=LMDB|publisher=Sampath Herga|access-date=2013-08-30|archive-url=https://web.archive.org/web/20130829025217/http://sampathherga.in/lmdb/|archive-date=2013-08-29|url-status=dead}} in various languages including Chinese.{{cite web | url=http://jianshu.io/p/yzFf8j|title=lmdb简介 - 简书}}

• Ordered Key-Value Store

{{reflist}}

Category:C (programming language) libraries

Category:Embedded databases

Category:Free software programmed in C

Category:Key-value databases

Category:NoSQL

Category:Structured storage