SET @start_global_value = @@global.alter_algorithm;
SELECT @@global.alter_algorithm;
@@global.alter_algorithm
DEFAULT
SET GLOBAL alter_algorithm=2;
Warnings:
Warning	4200	The variable '@@alter_algorithm' is ignored. It only exists for compatibility with old installations and will be removed in a future release
SELECT @@global.alter_algorithm;
@@global.alter_algorithm
DEFAULT
SET GLOBAL alter_algorithm=5;
ERROR 42000: Variable 'alter_algorithm' can't be set to the value of '5'
SELECT @@global.alter_algorithm;
@@global.alter_algorithm
DEFAULT
SET SESSION alter_algorithm=INSTANT;
Warnings:
Warning	4200	The variable '@@alter_algorithm' is ignored. It only exists for compatibility with old installations and will be removed in a future release
SHOW SESSION VARIABLES LIKE 'alter_algorithm';
Variable_name	Value
alter_algorithm	DEFAULT