In this blog post, I’ll look into four ways MySQL executes GROUP BY. 

In my previous blog post, we learned that indexes or other means of finding data might not be the most expensive part of query execution. For example, MySQL GROUP BY could potentially be responsible for 90% or more of the query execution time. 

The main complexity when MySQL executes GROUP BY is computing aggregate functions in a GROUP BY statement. How this works is shown in the documentation for UDF Aggregate Functions. As we see, the requirement is that UDF functions get all values that constitute the single group one …

Many of you have already heard about NoSQL databases and one of the the most used tool is Memcached, where you add a cache layer between the application and database. Since MySQL version 5.6, a new plugin is available to do the integration between MySQL and Memcached. On this article, we will learn how to install it on linux, and some basic configurations of it.

Pre-requirements:
Install libevent

Installation:
To install memcached support we will need to create a few tables responsible for MySQL and memcached integration. MySQL already includes the file which creates those tables (innodb_memcached_config.sql), you can find this file in a sub folder of your basedir. To discover where is your basedir, run the bellow command:

mysql> SHOW VARIABLES LIKE 'basedir';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| basedir       | /usr  | …

As we know, one of the most important config for InnoDB is the innodb_buffer_pool_size, it basically store the innodb data and indexes in memory, when MySQL receives a query and the InnoDB pages involved on that query are stored in the buffer, it does not need to go to the disk to return the result, which is much faster (memory speed vs disk speed).

As it is stored in memory, every time you restart your MySQL server it starts with a clean/empty buffer pool and usually it take some time to warm-up the buffer.
To speed up this process, we can configure 2 variables that will dump and reload the pages reference stored in the buffer, this is a new functionality added on MySQL 5.6 (it was presented on previous versions of Percona Server and MariaDB).

If you have your production server already running, we are going to set it to dump the content every time it shutdown:

SET GLOBAL innodb_buffer_pool_dump_at_shutdown = 1; …

This is the 150th edition of Log Buffer, the weekly review of database blogs. Someone accidentally left Dave Edwards‘ cage unlocked, and he escaped, thus leaving me with the pleasurable duty of compiling the 150th weekly Log Buffer.

Many people other than Dave are finding release this week. Giuseppe Maxia explains some details of MySQL’s New Release Model. Andrew Morgan announces a New MySQL Cluster Maintenance Release. Aleksandr Kuzminsky of the MySQL Performance …

Yesterday, The Pythian Group issued a press release about my book, Pythian’s partnership with Sun, and our new “MySQL Adoption Accelerator Package”. I am not a marketing guru, but I can tell you what we the package means in terms of new work that the MySQL teams have been doing.

Basically, the MySQL Adoption Accelerator Package combines customized training with a comprehensive audit of systems. The name “Adoption Accelerator” makes it sound like it’s only for new applications that are almost ready to go live. What the program actually does is have us evaluate your systems, and intensively train you in the areas you want and need. The program is designed to suit all your needs, whether it’s teaching you about one topic (say, query optimization) or an entire range of topics, from Architecture to ZFS (special issues with running MySQL on ZFS, that is, but that did not fit a cute …

(Note: updated with the presentation video on 11/15/2008)

At LISA 2008, I gave a presentation entitled “How to Stop Hating MySQL: Fixing Common Mistakes and Myths”.

The presentation slides can be downloaded as a PDF at:

http://technocation.org/files/doc/stophatingmysql.pdf

View the video online at http://technocation.org/node/646/play or download the 202.5 MB Flash video file (.flv) directly at http://technocation.org/node/646/download.

Here are some notes and links I referred to:

Technocation, Inc containing free videos, a MySQL podcast (currently on hiatus) and blog posts about MySQL.

…

It felt like the right time for us to look back at some useful commands for table maintenance that some of us may not have mastered as much as we might like to think.

In my post about gathering index statistics, I referred to OPTIMIZE TABLE, ANALYZE TABLE, and REPAIR TABLE — but I never explained in depth what the different commands do, and what the differences between them are. That is what I thought I would do with this post, focusing on InnoDB and MyISAM, and the differences in how they treat those commands. I will also look at different cases and see which one is right for in each case.

(more…)

At the 2008 MySQL Conference and Expo, The Pythian Group gave away EXPLAIN cheatsheets. They were very nice, printed in full color and laminated to ensure you can spill your coffee* on it and it will survive.

For those not at the conference, or those that want to make more, the file is downloadable as a 136Kb PDF at explain-diagram.pdf

* or tea, for those of us in the civilized world.

• http://en.oreilly.com/mysql2008/public/schedule/detail/874
• presented by Charles Lee of Hyperic
• Hyperic has the best performance with MySQL out of MySQL, Oracle, and Postgres in their application
• I suddenly remember hyperic was highly recommended above nagios in MySQL Conference Liveblogging: Monitoring Tools (Wednesday 5:15PM)
• performance bottleneck
  • the database
    • CPU
    • memory
  • IO …

The “sla” in mysqlsla stands for “statement log analyzer”. This does a much better job than mysqldumpslow of analyzing your slow query log. In fact, you can sort by many different parameters — by sheer number of times the query shows up in the slow query log, by the total or average query [...]