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[Maria-docs] Segmented Key Cache - About section
by Daniel Bartholomew 13 May '10

13 May '10

Hello everyone, I'm working on the documentation for the Segmented Key Cache, one of the new features in MariaDB 5.2. The documentation page will have "about", "syntax", and "example" sections. I've based the "About" section on the High-Level Description from the worklog ( http://askmonty.org/worklog/Server-Sprint/?tid=85 ) and from the description in the mysys/mf_keycache.c file in the source. Here is my first draft. I've changed the wording a bit to help it flow better and I've changed "partition" to "segment" in keeping with the official name. ---------------------------------------------------------------------- == About Segmented Key Cache == A segmented key cache is a collection of structures for regular MyISAM key caches called key cache segments. Segmented key caches mitigate one of the major problem of the simple key cache: thread contention for key cache lock (mutex). With regular key caches, every call of a key cache interface function must acquire this lock. Threads compete for this lock even when the file and pages they have acquired shared locks for are in the key cache buffers. When working with a segmented key cache any key cache interface function that needs only one page has to acquire the key cache lock only for the segment the page is assigned to. This makes the chances for threads not having to compete for the same key cache lock better. Any page from a file can be placed into a buffer of only one segment. The number of the segment is calculated from the file number and the position of the page in the file, and it's always the same for the page. Pages are evenly distributed among segments. The idea and the original code of the segmented key cache was provided by Fredrik Nylander from Stardoll.com. The code was extensively reworked, improved, and eventually merged into MariaDB by Igor Babaev from Monty Program. ---------------------------------------------------------------------- If there are any factual errors with the above, let me know. Improvements and suggestions are also welcome. One thing I'm not happy with is this sentence: "Threads compete for this lock even when the file and pages they have acquired shared locks for are in the key cache buffers." The original sentence from the worklog reads: So threads compete for this lock even in the case when they have acquired shared locks for the file and pages they want read from are in the key cache buffers. ... which is very confusing to me. If anyone has a better or more accurate rewording, please send it my way. Also, there's a note in the source code (lines 5018-5023 of mysys/mf_keycache.c) which states: Unfortunately if we use a partitioned key cache with N partitions for B-tree indexes we can't say that the chances becomes N times less. The fact is that any index lookup operation requires reading from the root page that, for any index, is always ascribed to the same partition. To resolve this problem we should have employed more sophisticated mechanisms of working with root pages. Do any of you have any opinions on whether or not this should be mentioned somewhere in the documentation? The only issue I have with mentioning it is that if I do, the first question that comes to my mind is: "If it is not N-times less, how much less is it?" I don't have an answer to that question (and math isn't one of my strengths). Next up will be the "Syntax" section. Thanks. -- Daniel Bartholomew Monty Program - http://askmonty.org

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Re: [Maria-docs] new mysqlbinlog option in MariaDB 5.2
by Daniel Bartholomew 11 May '10

11 May '10

On Fri, 7 May 2010 14:56:24 +0400 Sergey Petrunya <psergey(a)askmonty.org> wrote: Sergey> Hi Daniel, Sergey> Sergey> Here it is at last: Sergey> Sergey> On Fri, Apr 02, 2010 at 04:44:22PM -0400, Daniel Bartholomew Sergey> wrote: Daniel> I'm preparing documentation on mysqlbinlog for the MariaDB Daniel> 5.2. reference manual. Daniel> Daniel> From looking at the 'mysqlbinlog --help' output and comparing Daniel> it to the output of the version in 5.1.44 it looks like the Daniel> only command-line option that was added was Daniel> '--rewrite-db=name' (unless I'm missing something). Were any Daniel> other options added to mysqlbinlog? Sergey> None that I know of. Daniel> From the worklog Daniel> ( http://askmonty.org/worklog/Server-Sprint/?tid=36 ), it Daniel> looks like you were the MP developer who worked on it. Let me Daniel> know if I should ask someone else. Sergey> Yes, it was me from MP side. Sergey> Sergey> The net result is as follows: mysqlbinlog got a new option, Sergey> Sergey> --rewrite-db='db_from->db_to' Sergey> Sergey> which is very similar to replication slave option Sergey> Sergey> --replicate-rewrite-db=”from->to” Sergey> Sergey> Everything that is said about replicate-rewrite-db here: Sergey> http://dev.mysql.com/doc/refman/5.1/en/replication-options-slave.html#optio… Sergey> applies to --rewrite-db. Sergey> To rephrase it: for both options the following holds: Sergey> Sergey> - for events that are binlogged as statements, rewriting the Sergey> database constitutes changing statement's default database from Sergey> db1 to db2. There is no statement analysis or rewrite of any Sergey> kind, that is, if one specifies "db1.tbl" in the statement Sergey> explicitly, that occurence won't be changed to "db2.tbl". Sergey> Sergey> - Row-based events are rewritten correctly. Sergey> Sergey> For both slave and mysqlbinlog, filtering applies after the Sergey> database rewrites have been performed. By filtering, I mean Sergey> - --replicate-[do|ignore]-xxx options for slave Sergey> - --database option for mysqlbinlog. Sergey> Sergey> See also http://askmonty.org/wiki/Scratch/ReplicationOption for Sergey> a 'map' of various relevant options. Sergey> Sergey> Please ask more questions if the above is unclear. Sergey> Thanks for the information! I've used it to update the mysqlbinlog page on the wiki: http://askmonty.org/wiki/Manual:Mysqlbinlog The part dealing with --rewrite-db is at the bottom of the page (it's the last row in the big mysqlbinlog options table). Let me know if there are any errors or if you think something more should be added. Thanks again! -- Daniel Bartholomew Monty Program - http://askmonty.org

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[Maria-docs] MariaDB Release Process
by Daniel Bartholomew 05 May '10

05 May '10

FYI: I just updated the Release Process page on the wiki. I removed some outdated information and added some new information (such as sending a note to maria-docs(a)lists.launchpad.net when a tree is ready for release instead of to docs(a)askmonty.org) http://askmonty.org/wiki/Release_Process Take a look if you are interested and let me know of any errors or omissions. Thanks. -- Daniel Bartholomew Monty Program - http://askmonty.org

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[Maria-docs] New Maria Docs list
by Daniel Bartholomew 05 May '10

05 May '10

All, I've created a new "Maria Docs" Launchpad team and mailing list for documentation-related discussions (including things like documentation for current and upcoming releases of MariaDB, planning and discussion of the askmonty.org knowledgebase, and so on). The group is open to everyone. https://launchpad.net/~maria-docs Thanks! -- Daniel Bartholomew Monty Program - http://askmonty.org

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[Maria-docs] Maria Docs list
by Daniel Bartholomew 30 Apr '10

30 Apr '10

This is an initial posting to the Maria Docs list on Launchpad. I'm just testing the functionality and making sure the list is working as it should. Thanks. -- Daniel Bartholomew Monty Program - http://askmonty.org

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