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ImageMagick book
MythTV book
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Fri, 24 Apr 2009
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I spent the day at the Drizzle Developer Day at Sun's insane asylum campus. I'm not joking here, the campus was apparently a former insane asylum. First off I battled getting Drizzle to compile on Ubuntu 8.10, where the secret sauce appears to be to know about the drizzle-developer PPA. If you're using Ubuntu 8.10, add this to your sources.list and life will be a bit better:
deb http://ppa.launchpad.net/drizzle-developers/ppa/ubuntu intrepid main
deb-src http://ppa.launchpad.net/drizzle-developers/ppa/ubuntu intrepid main
After that compiling drizzle was pretty easy.
Tags for this post: mysql( )
posted at: 16:41 | path: /mysql | permanent link to this entry
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Mon, 11 Aug 2008
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In an effort to speed up my database updates, I've been looking for ways to batch some of my updates. CASE seems like the way to go:
mysql> create table bar(a tinyint, b tinyint);
Query OK, 0 rows affected (0.02 sec)
mysql> insert into bar(a) values(1), (2), (3), (4), (5);
Query OK, 5 rows affected (0.00 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from bar;
+------+------+
| a | b |
+------+------+
| 1 | NULL |
| 2 | NULL |
| 3 | NULL |
| 4 | NULL |
| 5 | NULL |
+------+------+
5 rows in set (0.00 sec)
mysql> update bar set b = case a
-> when 1 then 42
-> when 2 then 43
-> when 3 then 44
-> else 45
-> end;
Query OK, 5 rows affected (0.00 sec)
Rows matched: 5 Changed: 5 Warnings: 0
mysql> select * from bar;
+------+------+
| a | b |
+------+------+
| 1 | 42 |
| 2 | 43 |
| 3 | 44 |
| 4 | 45 |
| 5 | 45 |
+------+------+
5 rows in set (0.00 sec)
I see stuff online which warns not to forget the else, otherwise you get a default of null, so I guess I should bear that caveat in mind...
Tags for this post: mysql( )
posted at: 09:37 | path: /mysql | permanent link to this entry
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Wed, 07 May 2008
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I've been doing a lot of batch updates on one of my databases at home recently. show processlist says something like this:
mysql> show processlist;
+-------+------+---------------+--------------+---------+-------+----------+------------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+-------+------+---------------+--------------+---------+-------+----------+------------------------------------------|
| 18354 | root | maui:37403 | smtp_servers | Query | 57234 | Updating | update ips_218 set reverse_lookup = null |
| 22286 | root | maui:37348 | smtp_servers | Query | 38103 | Updating | update ips_80 set reverse_lookup = null, |
| 22851 | root | maui:54982 | smtp_servers | Query | 34091 | Updating | update ips_19 set reverse_lookup = null, |
| 23351 | root | molokai:58232 | smtp_servers | Sleep | 57 | | NULL |
| 23496 | root | maui:40923 | smtp_servers | Query | 29973 | Updating | update ips_62 set reverse_lookup = null, |
| 23906 | root | maui:38068 | smtp_servers | Query | 26794 | Updating | update ips_83 set reverse_lookup = null, |
| 25675 | root | maui:56438 | smtp_servers | Query | 12505 | Updating | update ips_82 set reverse_lookup = null, |
| 25846 | root | maui:41334 | smtp_servers | Query | 10948 | Updating | update ips_90 set reverse_lookup = null, |
| 26437 | root | maui:41139 | smtp_servers | Query | 6211 | Updating | update ips_66 set reverse_lookup = null, |
| 26773 | root | maui:32885 | smtp_servers | Query | 3526 | Updating | update ips_76 set reverse_lookup = null, |
| 27073 | root | maui:42607 | smtp_servers | Query | 1148 | Updating | update ips_11 set reverse_lookup = null, |
| 27202 | root | molokai:50688 | smtp_servers | Query | 0 | NULL | show processlist |
| 27203 | root | molokai:50689 | smtp_servers | Sleep | 2 | | NULL |
+-------+------+---------------+--------------+---------+-------+----------+------------------------------------------+
14 rows in set (0.20 sec)
Now, wouldn't it be nice if MySQL provided some extra information about the progress of those queries? Like for example the number of rows which have been updated so far, or an estimate of how long the query has left to run? I'm ok with such queries not being very accurate, but I assume the storage engine has to have some idea of how many rows are in the table and how many it has touched already.
Perhaps something like this already exists and I haven't noticed? I'm using innodb if that matters.
Update: it seems like innodb can answer this question for me:
mysql> show engine innodb status \G;
...
---TRANSACTION 0 40056, ACTIVE 39794 sec, process no 22984, OS thread id 3020733328 waiting in InnoDB queue
mysql tables in use 1, locked 1
6672 lock struct(s), heap size 748864, undo log entries 909825
MySQL thread id 22851, query id 351217 maui 192.168.1.93 root Updating
update ips_19 set reverse_lookup = null, reverse = null, reverse_extracted
...
That doesn't give you an estimate of percentage complete though. I assume there is a 1:1 correlation between undo row entries and rows altered by the query?
Update: my imperical observation is that the undo rows are not 100% correlated to the number of rows your query changed. Its correlated to the number of rows that were changed kinda near your query. For example, if you're doing an update, then the number is good enough to trust. However, if you're doing a select, then the number seems to be the number of rows someone else changed while your select was running (i.e. how many old versions needed to be kept around because of your select transaction).
Also, Jeremy Cole to the rescue!
Tags for this post: mysql( )
posted at: 11:19 | path: /mysql | permanent link to this entry
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Mon, 23 Jul 2007
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Apart from sniping the queries, is there any other way to reduce the amount of time that a query will wait before giving up on getting access to a locked table?
Tags for this post: mysql( )
posted at: 15:04 | path: /mysql | permanent link to this entry
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Sat, 12 May 2007
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Hi. I am doing a select like this in MySQL 5:
select * from foo where bar rlike '(.*),(.*)';
The specific example here is made up. Anyway, I'd like to be able to get to the matched text from bar, like I can with various languages regexp libraries. Is this functionality exposed at all in MySQL? I've looked at the docs and can't see any indication that it is, so this might just be wishful thinking.
Tags for this post: mysql( )
posted at: 08:17 | path: /mysql | permanent link to this entry
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Thu, 26 Apr 2007
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Mon, 23 Apr 2007
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Fri, 30 Mar 2007
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Tue, 06 Mar 2007
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I've been wanting a query sniper for a while for MySQL (some people seem to call them "query killers"). They're basically programs which inspect the MySQL "show processlist" command and decide to kill some processes if they violate specified rules. I have a prototype of one in python, and couldn't find any other implementations until tonight when I came across Querybane, which is what Wikipedia use to do exactly the same thing.
Now, I need to think further about if querybane does what I want, especially given I can't find the source code. Perhaps it's hidden in the media wiki code somewhere? The only code for a project named "servmon" (it's parent project) that I can find is four years old and in PHP.
(Oh, by the way, the Wikipedia MySQL docs are really interesting, for example this page has some nice practical advice about replication log corruption. I wish I had found this before now for two reasons: it's nice to see how other people do this stuff; and there is some stuff I can totally steal from here.)
So, does anyone know where I can find recent querybane code? Alternatively, what do other people use as a query sniper? Is it worth open sourcing mine?
Update: Apparently what I needed to do was sleep on it, and use Google Code Search. The querybane code appears to be at http://svn.wikimedia.org/svnroot/mediawiki/trunk/servmon/. In the end it's not going to work for me, as it seems to be really based around a world in which you use IRC to keep a track of the state of your servers, which isn't something I want to do.
Tags for this post: mysql( )
posted at: 11:03 | path: /mysql | permanent link to this entry
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Sat, 30 Dec 2006
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I was walking down Mountain View's Castro Street this afternoon, and noticed that meebo is advertising for developers and system admins. Interestingly, they seem to match the design pattern used by pretty much every web 2.0 company I have seen around here (except MySpace): linux, MySQL, and Ajax. So, there you go.
Tags for this post: mysql( )
posted at: 22:09 | path: /mysql | permanent link to this entry
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Wed, 22 Nov 2006
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Kynan and I came along to the MySQL camp, and thru a quirk of fate pretty much ended up running it (the person who was meant to be running it got injured on the first day and had to go off to hospital). In return we wrote the Google Code blog post about the event. Pretty cool, huh?
Tags for this post: mysql( )
posted at: 16:43 | path: /mysql | permanent link to this entry
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Wed, 10 May 2006
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Fri, 05 May 2006
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Three intrepid MySQLers came to Google after the user conference to give internal tech talks. They were kind enough to agree to us hosting them for other people to see. The first two are up, so I'll mention those now, and put a link to the last one when it's available...
Click on the thumbnail to be taken to the video.
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Jay Pipes is a co-author of the recently published Pro MySQL (Apress, 2005), which covers all of the newest MySQL 5 features, as well as in-depth discussion and analysis of the MySQL server architecture, storage engines, transaction processing, benchmarking, and advanced SQL scenarios. You can also see his name on articles appearing in Linux Magazine and can read more articles about MySQL at his website. Jay Pipes is MySQL's Community Relations Manager for North America.
Learn where to best focus your attention when tuning the performance of your applications and database servers, and how to effectively find the "low hanging fruit" on the tree of bottlenecks. It's not rocket science, but with a bit of acquired skill and experience, and of course good habits, you too can do this magic!
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Timour Katchaounov
The first part of this talk describes the main principles behind MySQL's query optimiser and execution engine, how the optimiser transforms queries into executable query plans, what these plans look like, and how they are executed.
The second part of the talk describes the major improvements in the query engine of MySQL 5.0, and how these improvements can benefit the users of MySQL 5.0. The "greedy" optimiser reduces compilation time for big queries with orders of magnitude. The "index merge" access method provides a way to use more than one index for the same query. For faster plan execution and to allow better join orders, the 5.0 optimiser transforms most outer joins into inner joins.
The outer joins that cannot be transformed into inner ones are executed in a pipeline manner, so that no intermediate results need to be materialised. Finally, some GROUP BY and DISTINCT queries can be executed much faster thanks to "loose index scan" technique that reads only a fraction of an index.
The talk concludes with the near-future plans for new features coming in the next versions of MySQL.
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Stewart Smith works for MySQL AB as a software engineer working on MySQL Cluster. He is an active member of the free and open source software community, especially in Australia. Although Australian, he does not dress like Steve Irwin—although if he wrestled crocodiles he probably would. He is a fan of great coffee, great beer, and is currently 39,000 feet above sea level.
part 1 - Introduction to MySQL Cluster The NDB storage engine (MySQL Cluster) is a high-availability storage engine for MySQL. It provides synchronous replication between storage nodes and many mysql servers having a consistent view of the database. In 4.1 and 5.0 it's a main memory database, but in 5.1 non-indexed attributes can be stored on disk. NDB also provides a lot of determinism in system resource usage. I'll talk a bit about that.
part 2 - new features in 5.1 including cluster to cluster replication, disk based data and a bunch of other things. anybody that is attending the mysql users conference may find this eerily familiar.
I can also talk about latest-and-totally-greatest developments and future stuff we're working on. i can also take questions and constructive abuse :)
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You can see a complete list of the MySQL tech talks at Google here.
Update: added Stewart's talk now that it is online.
Tags for this post: mysql( )
posted at: 10:06 | path: /mysql | permanent link to this entry
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Tue, 25 Apr 2006
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So, I attended the first day of the MySQL user's conference yesterday, which was the tutorial day. Overall I was fairly impressed. Registration was easy, the actual rooms presentations are given in are comfortable, the PA system seemed to work after some initial problems in the morning tutorial I attended.
The conference center seems to be big on retirees hanging around, which I thought was weird. Each room comes with a little old lady, whose job appears to be to read a fiction novel at the door. I really have no idea what else they were achieving. They seemed to be having fun though. I did find it a bit odd that the only drinks provided by the catering staff during the day were acidic, and most of them caffinated. For example, we had choices between coffee, tea, soda water, coke, diet coke, pepsi and diet pepsi. Some fruit juice or even plain water would have been a nice change by the end of the day.
The food was good, unless you're a vegan like Stewart at which time the catering staff looked confused and had to go off and get him something special (which didn't look all that special to me when it came ten minutes later). If that happens again today, then I might try to talk him into just going to a restaurant for lunch with me.
The first tutorial I attended was about MySQL cluster, and to be honest I kinda lost interest at the point where I found out that the database currently has to store all of it's data in RAM. That basically renders it unusable for anyone with a large-ish database. The speaker did a good job in adverse circumstances such as the PA system initially not working, and trying to speak in a language which is not his native tongue in a room which was very wide. I do think that he needed to clamp down harder on the irrelevant, repetitive and self serving questions though. It seemed to me that there were a fair few people in the room who viewed the conference as their chance to get someone else to fix their problems at work. Whilst it's fair to go to a conference to ask advice on problems you're having, I do think that some research prior to attending (or even using the wireless during the conference) is a good idea, and that you shouldn't interrupt the flow of a talk to ask your tangential questions.
The second tutorial was by a Yahoo, and was on MySQL replication. It was excellent -- well prepared, relevant to what I am caring about at the moment, coherent, and flowed well. Jeremy and Eric did a great job (slides from the talk). I hung around at the end to try to offer them beer, but they were swamped by fans who didn't appear to want to leave. I'll have to chase them down today sometime to make the offer.
Overall, not a perfect start to the conference, but I thought the day was very useful. A good first day.
Tags for this post: mysql( ) conference( ) mysqluc2006( )
posted at: 14:45 | path: /mysql/conference/mysqluc2006 | permanent link to this entry
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So, I attended the first day of the MySQL user's conference yesterday, which was the tutorial day. Overall I was fairly impressed. Registration was easy, the actual rooms presentations are given in are comfortable, the PA system seemed to work after some initial problems in the morning tutorial I attended.
The conference center seems to be big on retirees hanging around, which I thought was weird. Each room comes with a little old lady, whose job appears to be to read a fiction novel at the door. I really have no idea what else they were achieving. They seemed to be having fun though. I did find it a bit odd that the only drinks provided by the catering staff during the day were acidic, and most of them caffinated. For example, we had choices between coffee, tea, soda water, coke, diet coke, pepsi and diet pepsi. Some fruit juice or even plain water would have been a nice change by the end of the day.
The food was good, unless you're a vegan like Stewart at which time the catering staff looked confused and had to go off and get him something special (which didn't look all that special to me when it came ten minutes later). If that happens again today, then I might try to talk him into just going to a restaurant for lunch with me.
The first tutorial I attended was about MySQL cluster, and to be honest I kinda lost interest at the point where I found out that the database currently has to store all of it's data in RAM. That basically renders it unusable for anyone with a large-ish database. The speaker did a good job in adverse circumstances such as the PA system initially not working, and trying to speak in a language which is not his native tongue in a room which was very wide. I do think that he needed to clamp down harder on the irrelevant, repetitive and self serving questions though. It seemed to me that there were a fair few people in the room who viewed the conference as their chance to get someone else to fix their problems at work. Whilst it's fair to go to a conference to ask advice on problems you're having, I do think that some research prior to attending (or even using the wireless during the conference) is a good idea, and that you shouldn't interrupt the flow of a talk to ask your tangential questions.
The second tutorial was by a Yahoo, and was on MySQL replication. It was excellent -- well prepared, relevant to what I am caring about at the moment, coherent, and flowed well. Jeremy and Eric did a great job (slides from the talk). I hung around at the end to try to offer them beer, but they were swamped by fans who didn't appear to want to leave. I'll have to chase them down today sometime to make the offer.
Overall, not a perfect start to the conference, but I thought the day was very useful. A good first day.
Tags for this post: mysql( ) mysqluc( )
posted at: 14:45 | path: /mysql/mysqluc | permanent link to this entry
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