SET @start_global_value = @@global.key_cache_segments;
select @@global.key_cache_segments;
@@global.key_cache_segments
0
select @@session.key_cache_segments;
ERROR HY000: Variable 'key_cache_segments' is a GLOBAL variable
show global variables like 'key_cache_segments';
Variable_name	Value
key_cache_segments	0
show session variables like 'key_cache_segments';
Variable_name	Value
key_cache_segments	0
select * from information_schema.global_variables where variable_name='key_cache_segments';
VARIABLE_NAME	VARIABLE_VALUE
KEY_CACHE_SEGMENTS	0
select * from information_schema.session_variables where variable_name='key_cache_segments';
VARIABLE_NAME	VARIABLE_VALUE
KEY_CACHE_SEGMENTS	0
set global key_cache_segments=1;
select @@global.key_cache_segments;
@@global.key_cache_segments
1
set session key_cache_segments=1;
ERROR HY000: Variable 'key_cache_segments' is a GLOBAL variable and should be set with SET GLOBAL
set global key_cache_segments=1.1;
ERROR 42000: Incorrect argument type to variable 'key_cache_segments'
set global key_cache_segments=1e1;
ERROR 42000: Incorrect argument type to variable 'key_cache_segments'
set global key_cache_segments="foo";
ERROR 42000: Incorrect argument type to variable 'key_cache_segments'
set global key_cache_segments=0;
select @@global.key_cache_segments;
@@global.key_cache_segments
0
set global key_cache_segments=cast(-1 as unsigned int);
Warnings:
Note	1105	Cast to unsigned converted negative integer to it's positive complement
Warning	1292	Truncated incorrect key_cache_segments value: '18446744073709551615'
select @@global.key_cache_segments;
@@global.key_cache_segments
64
SET @@global.key_cache_segments = @start_global_value;