Quite often we need to perform a so-called “MySQL instance audit”. This common DBA procedure should give you a general view of the MySQL environment. You may be interested in a basic understanding of what kind of operation MySQL performs, how much memory does it use, or how well does it look from the performance point of view. There is no easy out-of-the-box way to do such an audit on a MySQL server. You can use SHOW STATUS and check the list of system variables, but this way can hardly be called DBA-friendly.

Fortunately there are several tools to make this process easier. Among most popular are mysqlreport and MySQLTuner. In this post I’d like to give a brief overview of MySQLTuner.

So, what can MySQLTuner do? Quoting the documentation: “MySQLTuner is a script written in Perl that will assist you with your MySQL configuration and make recommendations for increased performance and stability. Within seconds, it will display statistics about your MySQL installation and the areas where it can be improved.”

It’s not magic — they don’t use any “hidden” or unknown MySQL features to provide the report. What they do is use SHOW STATUS metrics and provide a user-friendly report, interpreting data this or that way. What makes such tools really valuable is the way they interpret that data.

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Note: This article is about the WHERE extension to SHOW. I specifically use SHOW STATUS as an example, but WHERE is an extension to many SHOW statements.

Often DBAs will assess the health of a system by looking at some of the status variables returned by SHOW GLOBAL STATUS (specifying GLOBAL is important; remember that SHOW STATUS is the same as SHOW SESSION STATUS).

There are many status variables that SHOW GLOBAL STATUS returns. (SHOW GLOBAL STATUS on a Windows machine, MySQL version 5.0.67 returned 249, 5.1.22 returned 256 and 6.0.6-alpha returned 295 status variables!). I have used the SHOW STATUS LIKE syntax to help give me the output I really want, particularly when I forget the exact names of the status variables I am looking for.

But I did not know of a way to perform SHOW STATUS NOT LIKE or have any other means of filtering the information. Until today, when I was reading up on SHOW STATUS.
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