select @@global.performance_schema_max_file_classes; @@global.performance_schema_max_file_classes 123 select @@session.performance_schema_max_file_classes; ERROR HY000: Variable 'performance_schema_max_file_classes' is a GLOBAL variable show global variables like 'performance_schema_max_file_classes'; Variable_name Value performance_schema_max_file_classes 123 show session variables like 'performance_schema_max_file_classes'; Variable_name Value performance_schema_max_file_classes 123 select * from information_schema.global_variables where variable_name='performance_schema_max_file_classes'; VARIABLE_NAME VARIABLE_VALUE PERFORMANCE_SCHEMA_MAX_FILE_CLASSES 123 select * from information_schema.session_variables where variable_name='performance_schema_max_file_classes'; VARIABLE_NAME VARIABLE_VALUE PERFORMANCE_SCHEMA_MAX_FILE_CLASSES 123 set global performance_schema_max_file_classes=1; ERROR HY000: Variable 'performance_schema_max_file_classes' is a read only variable set session performance_schema_max_file_classes=1; ERROR HY000: Variable 'performance_schema_max_file_classes' is a read only variable