Lightning Memory-Mapped Database: Difference between revisions

Revision as of 11:08, 26 September 2023

Revision as of 11:09, 26 September 2023

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== Technical reviews of LMDB ==

LMDB makes novel use of well-known computer science techniques such as [[copy-on-write]] semantics and [[B+ tree]]s to provide atomicity and reliability guarantees as well as performance that can be hard to accieveaccept, 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<ref>{{cite web | url=http://banksco.de/p/lmdb-the-leveldb-killer.html|title=LMDB: The Leveldb Killer?}}</ref> ''(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.<ref>{{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}}</ref>)''

The presentation did spark other database developers to dissect the code in-depth to understand how and why it works. Reviews run from brief <ref>{{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}}</ref> 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.<ref>{{cite web | url=http://ayende.com/blog/162754/reviewing-lightning-memory-mapped-database-library-partial|title=Reviewing Lightning memory-mapped database library: Partial}}</ref> This review, conducted by a .NET developer with no former experience of [[C (programming language)|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".<ref>{{cite web | url=http://ayende.com/blog/162917/some-final-notes-about-lmdb-review|title=Some final notes about LMDB review}}</ref>