Query optimization is the first and most important task of MySQL performance. Experts agree: "[Tuning] queries (and schemas) can often give you 1000-fold performance increase" (High Performance MySQL). If you are serious about MySQL performance then you must be serious about query optimization. The following documents are detailed examples of optimizing various aspects of slow queries:

• Indexing Basic MySQL Queries
• Table Design and MySQL Index Details
• MySQL ORDER BY With LIMIT and ANALYZE
• How To Index For MySQL Joins
• How To Look At MySQL Joins and More ORDER BY With LIMIT

For non-technical users, Non-technical Guide to Isolating Slow MySQL Queries outlines how to get the best information to handoff to a MySQL expert who can fix the slow queries for you.

If MySQL performance truly interests you then you will probably reach a point where simply knowing that something works is not enough; you need to understand the intricate details of why it works. The following documents investigate the intricate details of various MySQL issues:

• COM_QUIT and Questions: Why COM_QUIT makes Questions add up (almost) exactly.
• DNS Details: How MySQL really uses DNS and handles slow or failing nameservers.
• Select and Sort Status Variables: The meaning and cause of each MySQL Select and Sort status variable.
• JOIN Rows Produced vs. Rows Read: The effect of different JOIN plans on the number of rows produced verses rows read.
• Slow Log and long_query_time Microsecond Resolution: A summary of microsecond resolution slow query logging support in MySQL.