Baron makes an excellent point in Why you should ignore MySQL’s key cache hit ratio — ratio is not the same as rate. Furthermore, rate is [often] the important thing to look at.

This is something that, at Pythian, we internalized a long time ago when thinking about MySQL tuning. In fact, mysqltuner 2.0 takes this into account, and the default configuration includes looking at both ratios and rates.

If I told you that your database had a ratio of temporary tables written to disk of 20%, you might think “aha, my database is slow because of a lot of file I/O caused by writing temporary tables to disk!”. However, that 20% ratio may actually mean a rate of 2 per hour — which is most likely …

A special extended edition of Tech Messages for 2010-02-20 through 2010-02-24:

• Gartner EXP Worldwide Survey of Nearly 1,600 CIOs Shows IT Budgets in 2010 to be at 2005 Levels
  Virtualization tops the technology priorities.
• Cisco Offers Three-Year, Zero-Percent Financing to U.S. Small and Medium-Sized Businesses -> Cisco News
• Marc Alff's blog: Performance schema overview
  Really interesting stuff for MySQL developers.
• …

In MySQL significant performance improvements can be achieved by the correct use of indexes. It is important to understand different MySQL index implementations and one key improvement on indexes defined on single columns is to use multiple column or more commonly known concatenated indexes.

However it’s also possible to define ineffective indexes. This example shows you how to identify a concatenated index that is ineffective.

CREATE TABLE example (
  id INT UNSIGNED NOT NULL AUTO_INCREMENT,
  a  INT UNSIGNED NOT NULL,
  b  INT UNSIGNED NOT NULL,
  c  INT UNSIGNED NOT NULL,
  d  INT UNSIGNED NOT NULL,
  x  VARCHAR(10),
  y  VARCHAR(10),
  z  VARCHAR(10),
PRIMARY KEY (id),
UNIQUE INDEX (a,b,c,d)
) ENGINE=InnoDB;

INSERT INTO example(a,b,c,d) VALUES
(1,0,1,1),(1,0,1,2), (1,0,2,3), (1,0,4,5),
(2,0,2,1),(2,0,2,2), …

Cary Millsap has a concise, readable paper on performance. Anyone involved in database performance optimization should read it. Cary’s writing has heavily influenced the mk-query-digest tool for analyzing MySQL/PostgreSQL/Memcached/HTTP query performance, and I think you’ll get a lot more from mk-query-digest if you read this paper — and you should also read his book, reviewed here. It’s one of the top books on my Essential Books List.

Related posts:

1. …

There are those that are very adamant about letting people know that using INFORMATION_SCHEMA can crash your database. For example, in making changes to many tables at once Baron writes:

“querying the INFORMATION_SCHEMA database on MySQL can completely lock a busy server for a long time. It can even crash it. It is very dangerous.”

Though Baron is telling the truth here, he left out one extremely important piece of information: you can actually figure out how dangerous your INFORMATION_SCHEMA query will be, ahead of time, using EXPLAIN.

In MySQL 5.1.21 and higher, not only were optimizations made to the INFORMATION_SCHEMA, but new values were added so that EXPLAIN had better visibility into what MySQL is actually doing. As per …

This Thursday (February 18th, 17:00 UTC - note the different starting time!), Marc Alff will present the brand new Performance Schema: Instrumenting Code. Marc is the implementor of the Performance Schema feature. His presentation will show how developers maintaining

• the MySQL server code,
• a storage engine,
• or any type of plugin

can instrument the code to collect data for the new performance schema instrumentation.

For MySQL University sessions, point your browser to this page. You need a browser with a working Flash plugin. You may register for a Dimdim account, but you don't have to. (Dimdim is the …

This Thursday (February 18th, 17:00 UTC - note the different starting time!), Marc Alff will present the brand new Performance Schema: Instrumenting Code. Marc is the implementor of the Performance Schema feature. His presentation will show how developers maintaining

• the MySQL server code,
• a storage engine,
• or any type of plugin

can instrument the code to collect data for the new performance schema instrumentation.

For MySQL University sessions, point your browser to this page. You need a browser with a working Flash plugin. You may register for a Dimdim account, but you don't have to. (Dimdim is the …

This Thursday (February 18th, 17:00 UTC - note the different starting time!), Marc Alff will present the brand new Performance Schema: Instrumenting Code. Marc is the implementor of the Performance Schema feature. His presentation will show how developers maintaining

• the MySQL server code,
• a storage engine,
• or any type of plugin

can instrument the code to collect data for the new performance schema instrumentation.

For MySQL University sessions, point your browser to this page. You need a browser with a working Flash plugin. You may register for a Dimdim account, but you don't have to. (Dimdim is the …

The slides for my presentation at FOSDEM 2010 are now available online at slideshare. In this presentation I describe a successful client implementation with the result of 10x performance improvements. My presentation covers monitoring, reviewing and analyzing SQL, the art of indexes, improving SQL, storage engines and caching.

The end result was a page load improvement from 700+ms load time to a a consistent 60ms.

10x Performance Improvements – A Case Study View more presentations from Ronald Bradford.

I’ve recently become supremely disappointed in the availability of Nagios checks for RAID cards. Too often, I see administrators rely on chance (or their hosting provider) to discover failed drives, a dying BBU, or a degrading capacity on their RAID cards. So I began work on check_raid (part of check_mysql_all) to provide a suite of [...]