select @@global.innodb_read_io_threads; @@global.innodb_read_io_threads 2 select @@session.innodb_read_io_threads; ERROR HY000: Variable 'innodb_read_io_threads' is a GLOBAL variable show global variables like 'innodb_read_io_threads'; Variable_name Value innodb_read_io_threads 2 show session variables like 'innodb_read_io_threads'; Variable_name Value innodb_read_io_threads 2 select * from information_schema.global_variables where variable_name='innodb_read_io_threads'; VARIABLE_NAME VARIABLE_VALUE INNODB_READ_IO_THREADS 2 select * from information_schema.session_variables where variable_name='innodb_read_io_threads'; VARIABLE_NAME VARIABLE_VALUE INNODB_READ_IO_THREADS 2 set global innodb_read_io_threads=1; ERROR HY000: Variable 'innodb_read_io_threads' is a read only variable set session innodb_read_io_threads=1; ERROR HY000: Variable 'innodb_read_io_threads' is a read only variable