set @save.slave_parallel_workers= @@global.slave_parallel_workers; select @@session.slave_parallel_workers; ERROR HY000: Variable 'slave_parallel_workers' is a GLOBAL variable select variable_name from information_schema.global_variables where variable_name='$var'; variable_name select variable_name from information_schema.session_variables where variable_name='$var'; variable_name set @@global.slave_parallel_workers= 0; select @@global.slave_parallel_workers; @@global.slave_parallel_workers 0 set @@global.slave_parallel_workers= 1.1; ERROR 42000: Incorrect argument type to variable 'slave_parallel_workers' set @@global.slave_parallel_workers= "foo"; ERROR 42000: Incorrect argument type to variable 'slave_parallel_workers' set @@global.slave_parallel_workers= 0; set @@global.slave_parallel_workers= cast(-1 as unsigned int); Warnings: Warning 1292 Truncated incorrect slave_parallel_workers value: '18446744073709551615' select @@global.slave_parallel_workers as "truncated to the maximum"; truncated to the maximum 1024 set @@global.slave_parallel_workers= @save.slave_parallel_workers;