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.

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

Sergey from the MySQL Optimizer team talks about recent developments in the MySQL Optimizer, including: What's new in MySQL 5.1 optimizer, Overview of known optimizer problems in MySQL 5.1, State of new optimizations in MySQL 6.0, Optimizer development beyond 6.0