Announced on Sunday at Oracle Open World 2011 is the release of the Effective MySQL book series starting with the “Optimizing SQL Statements” title. The goal of the Effective MySQL series is a highly practical, concise and topic specific reference providing applicable knowledge to use on each page. A feedback comment provided today was “no fluff” which is great comment to re-enforce the practical nature of the series.

Details on the Effective MySQL Optimizing SQL Statements page include a sample chapter, code downloads and purchase links for print and e-books at …

I will be joining a stellar class of speakers at the Insight Out DB Showcase in Tokyo from Oct 19-21, 2011. This event covers several RDBMS technologies including MySQL.

My topics are:

• Better MySQL Security and Administration
• Mastering MySQL Performance Tuning

I recently gave a presentation at the New York Effective MySQL Meetup on the new features of, and some of the compelling reasons to upgrade to MySQL 5.5. There are also a number of new MySQL variables that can have a dramatic effect on performance in a highly transactional environment, innodb_buffer_pool_instances and innodb_purge_threads are just two to consider.

For more information on all the new variables, status, reserved words and benchmarks of new features you can Download Presentation Slides.

Historically it was considered that MySQL will generally use only one index per referenced table in a SQL query. In MySQL 5.0 the introduction of merge indexes enabled for certain conditions the possibility to utilize two indexes however this could result in worst performance then creating a better index. In MySQL 5.1 it became possible to control optimization switches with the optimizer_switch system variable.

However in explaining how to utilize the intersection, union and sort union in queries I discovered that MySQL could use three indexes for one given table.

        Extra: Using union(name,intersect(founded,type)); Using where

I was not aware of this.

Many people consider this information in the MySQL Query Execution Plan (QEP) to indicate that the referenced table is using an index. It actually means that ONLY the index is used. This can for larger and more frequent queries provide a significant boost.

In a recent example, adding an index dropped a query from 190ms to 6ms. However adding a better index dropped that 6ms query to 1.2ms. When executed 100s/1000s of times per second these millisecond improvements can have a huge benefit in greater scalability. While people often tune slow running queries, in a well tuned system shaving milliseconds of queries, in this example making 6ms query 80% better is a far greater improvement.

You can get a detailed explanation of how to identify, create and verify covering indexes from my Percona Live presentation Improving performance …

Today was another example of where a correct SQL_MODE saved customer data from being corrupted. By default, MySQL does not enforce data integrity. It allows what is called silent truncations where the result of what you INSERT or UPDATE does not represent truth. NOTE: I see very few customers ever have this correctly configured, those that do have actually listened to my advice.

If you do not read any further, your production MySQL environments should be running with at the bare minimum of SQL_MODE=STRICT_ALL_TABLES however I would also advocate for additional SQL_MODE settings.

For this example, some modified undesirable code attempted to reduce a counter by 1, however because of an UNSIGNED data type and a correctly set SQL_MODE, the application produced an error and data was not corrupted.

This is what should happen with your SQL.

mysql> update stats set loss_count=loss_count - 1 where user_id=42; …

Today we have a dedicated MySQL conference in New York with Percona Live. It is great to see an overflowing room in the opening keynote. With over 20 speakers and 4 dedicated tracks there is a lot of content for attendees.

With all the confusion over conference ownership since the Oracle acquisition I applaud Percona for taking an initiative, first in San Francisco and now here in New York. Also announced today is the next Percona Live in London which is great for the MySQL ecosystem in Europe.

My list of reasons for never using or recommending Amazon’s MySQL RDS service grows every time I experience problems with customers. This was an interesting and still unresolved issue.

ERROR 126 (HY000): Incorrect key file for table '/rdsdbdata/tmp/#sql_5b7_1.MYI'; try to repair it

You may see this is a MyISAM table. The MySQL database is version 5.5, all InnoDB tables and is very small 100MB in total size.
What is happening is that MySQL is generating a temporary table, and this table is being written to disk. I am unable to change the code to improve the query causing this disk I/O.

What I can not understand and have no ability to diagnose is why this error occurs sometimes and generally when the database is under additional system load. With RDS you have no visibility of the server running the production database. While you have SQL access, an API for managing MySQL configuration options (I also add not all …

Last week at the OUG Harmony conference thanks to Dimitri Kravtchuk I learned that setting query_cache_size=0 does not disable and remove locking from the Query Cache. You actually need to also set query_cache_type=0. This appears to been a bug, seen in the presently still open MySQL bugs database entry #38511.

My recommendation to customers now is to set both variables on all existing MySQL versions if you are not using the MySQL Query Cache.

Thanks to the Performance Schema in MySQL 5.5 for uncovering this. More information in Dimitri’s detailed post at MySQL Performance: Using Performance Schema

Details of all MySQL presentations at …

As the top MySQL expert in New York it is great to join the team at Percona for the upcoming Percona Live in New York City on May 26th. As an invited speaker I am joining a select list of expert speakers including Harrison Fisk from Facebook, Kurt von Finck from Monty Program and Monty Taylor from the core Drizzle team.

My presentation will be on Improving Performance with Better Indexes where I will not only show how to apply indexes to improve query performance, but how to apply better indexes and provide even greater performance gains via a great technique known as a covering index.