The performance_schema database

In the most relevant parts of MariaDB code, instrumentations can be found that allow detailed performance monitoring. The results of such monitoring are written into a special database called performance_schema. Since the monitoring activity sensibly slows down the server performance, it is possible to disable it in the configuration file, by setting the performance_schema variable to 0.

The performance_schema variable is based on the following concepts:

To determine what the server must monitor, the performance_schema setup tables can be modified: setup_actors, setup_consumers, setup_instruments, and setup_objects. When a low-level operation takes place and performance_schema is enabled, if the involved actor, consumer, instrument, and object is monitored, new information is written into the performance_schema. A setup_timer table determines the granularity of the timers that are used to monitor various events (microseconds, nanoseconds, and so on).

The performance_schema setup table consists of several tables. However, the names of the most important ones follow a pattern, based on a prefix and suffix. The prefix indicates what type of information the table provides. The most important prefixes are:

The suffix indicates how the information is aggregated, shown as follows:

Other suffixes exist, but are self-explanatory.

For example, the events_waits_current table lists the threads that are currently waiting for an event. The events_statements_history table shows information about the recently executed statements.