1select @@global.back_log; 2@@global.back_log 380 4select @@session.back_log; 5ERROR HY000: Variable 'back_log' is a GLOBAL variable 6show global variables like 'back_log'; 7Variable_name Value 8back_log 80 9show session variables like 'back_log'; 10Variable_name Value 11back_log 80 12select * from information_schema.global_variables where variable_name='back_log'; 13VARIABLE_NAME VARIABLE_VALUE 14BACK_LOG 80 15select * from information_schema.session_variables where variable_name='back_log'; 16VARIABLE_NAME VARIABLE_VALUE 17BACK_LOG 80 18set global back_log=1; 19ERROR HY000: Variable 'back_log' is a read only variable 20set session back_log=1; 21ERROR HY000: Variable 'back_log' is a read only variable 22