You can answer many questions about a MySQL server by
inspecting its status. MySQL exposes information about server internals in
several ways. The newest is the
PERFORMANCE_SCHEMA database in MySQL 5.5, but
database has existed since MySQL 5.0, and there are a series of
SHOW commands that have existed practically
forever. Some information you can get via
SHOW commands isn’t found in the
The challenges for you are determining what is relevant to your problem, how to get the information you need, and how to interpret it. Although MySQL lets you see a lot of information about what’s going on inside the server, it’s not always easy to use that information. Understanding it requires patience, experience, and ready access to the MySQL manual. Good tools are helpful, too.
This appendix is mostly reference material, but you will also find some information on the functioning of server internals, especially in the sections on InnoDB.
MySQL exposes many system variables through the
SHOW VARIABLES SQL
command, as variables you can use in expressions, or with
mysqladmin variables at the command line. From MySQL 5.1, you can also access
them through tables in the
These variables represent a variety of configuration information,
such as the server’s default storage engine (
storage_engine), the available time zones, the connection’s collation, and startup parameters. ...