25.12.14 Performance Schema Status Variable Tables
The value of the
show_compatibility_56 system variable affects the information available from the tables described here. For details, see the description of that variable in Section 5.1.7, “Server System Variables”.
The MySQL server maintains many status variables that provide information about its operation (see Section 5.1.9, “Server Status Variables”). Status variable information is available in these Performance Schema tables:
global_status: Global status variables. An application that wants only global values should use this table.
session_status: Status variables for the current session. An application that wants all status variable values for its own session should use this table. It includes the session variables for its session, as well as the values of global variables that have no session counterpart.
status_by_thread: Session status variables for each active session. An application that wants to know the session variable values for specific sessions should use this table. It includes session variables only, identified by thread ID.
There are also summary tables that provide status variable information aggregated by account, host name, and user name. See Section 18.104.22.168, “Status Variable Summary Tables”.
The Performance Schema collects statistics for global status variables only for threads for which the
INSTRUMENTED value is
YES in the
threads table. Statistics for session status variables are always collected, regardless of the
The Performance Schema does not collect statistics for
Com_ status variables in the status variable tables. To obtain global and per-session statement execution counts, use the
events_statements_summary_by_thread_by_event_name tables, respectively. For example:
SELECT EVENT_NAME, COUNT_STAR FROM performance_schema.events_statements_summary_global_by_event_name WHERE EVENT_NAME LIKE 'statement/sql/%';
status_by_thread table contains the status of each active thread. It has these columns:
The thread identifier of the session in which the status variable is defined.
The status variable name.
The session variable value for the session named by the
status_by_thread table contains status variable information only about foreground threads. If the
performance_schema_max_thread_instances system variable is not autoscaled (signified by a value of -1) and the maximum permitted number of instrumented thread objects is not greater than the number of background threads, the table will be empty.
The Performance Schema supports
TRUNCATE TABLE for status variable tables as follows:
global_status: Resets thread, account, host, and user status. Resets global status variables except those that the server never resets.
session_status: Not supported.
status_by_thread: Aggregates status for all threads to the global status and account status, then resets thread status. If account statistics are not collected, the session status is added to host and user status, if host and user status are collected.
Account, host, and user statistics are not collected if the
performance_schema_users_sizesystem variables, respectively, are set to 0.
FLUSH STATUS adds the session status from all active sessions to the global status variables, resets the status of all active sessions, and resets account, host, and user status values aggregated from disconnected sessions.