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
select @@innodb_read_io_threads into @n;
set global innodb_read_io_threads = 1;
select @@innodb_read_io_threads;
@@innodb_read_io_threads
1
set global innodb_read_io_threads=64;
select @@innodb_read_io_threads;
@@innodb_read_io_threads
64
set session innodb_read_io_threads=1;
ERROR HY000: Variable 'innodb_read_io_threads' is a GLOBAL variable and should be set with SET GLOBAL
set global innodb_read_io_threads=@n;