MySQL 8.0 Reference Manual
MySQL 8.0 Release Notes
的MySQL server maintains many system variables that indicate how it is configured (seeServer System Variables). System variable information is available in these Performance Schema tables:
global_variables: Global system variables. An application that wants only global values should use this table.session_variables: System variables for the current session. An application that wants all system 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.variables_by_thread: Session system 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.persisted_variables: Provides a SQL interface to themysqld-auto.cnffile that stores persisted global system variable settings. SeeSection 10.14.1, “Performance Schema persisted_variables Table”.variables_info: Shows, for each system variable, the source from which it was most recently set, and its range of values. SeeSection 10.14.2, “Performance Schema variables_info Table”.
的SENSITIVE_VARIABLES_OBSERVERprivilege is required to view the values of sensitive system variables in these tables.
的session variable tables (session_variables,variables_by_thread) contain information only for active sessions, not terminated sessions.
的global_variablesandsession_variablestables have these columns:
VARIABLE_NAME的system variable name.
VARIABLE_VALUE的system variable value. For
global_variables, this column contains the global value. Forsession_variables, this column contains the variable value in effect for the current session.
的global_variablesandsession_variablestables have these indexes:
Primary key on (
VARIABLE_NAME)
的variables_by_threadtable has these columns:
THREAD_ID的thread identifier of the session in which the system variable is defined.
VARIABLE_NAME的system variable name.
VARIABLE_VALUE的session variable value for the session named by the
THREAD_IDcolumn.
的variables_by_threadtable has these indexes:
Primary key on (
THREAD_ID,VARIABLE_NAME)
的variables_by_threadtable contains system variable information only about foreground threads. If not all threads are instrumented by the Performance Schema, this table misses some rows. In this case, thePerformance_schema_thread_instances_loststatus variable is greater than zero.
TRUNCATE TABLEis not supported for Performance Schema system variable tables.