#
# show the global and session values;
#
select @@global.back_log;
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
select @@session.back_log;
show global variables like 'back_log';
show session variables like 'back_log';
--disable_warnings
select * from performance_schema.global_variables where variable_name='back_log';
select * from performance_schema.session_variables where variable_name='back_log';
--enable_warnings

#
# show that it's read-only
#
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
set global back_log=1;
--error ER_INCORRECT_GLOBAL_LOCAL_VAR
set session back_log=1;