Server Administration - MySQL - page 759

[mysqld]
character_set_server=utf8
sql_mode=TRADITIONAL
event_scheduler=1
innodb_buffer_pool_size=256M
Those are just suggestions; adjust the server configuration for your own requirements.
For information about plug-in and logging options in particular, see Recipes 22.2 and
22.3 .
Configuration control and verification at runtime
After the server starts, you can make runtime adjustments by changing system variables
using the SET statement:
SET GLOBAL var_name = value ;
That statement sets the global value of var_name ; that is, the value that applies to all
clients by default. Changes to the global value at runtime require the SUPER privilege.
Many system variables also have a session value, which is the value specific to a particular
client session. The session value of a given variable is initialized from the global value
when the client connects, but the client can change it thereafter. For example, the DBA
might set the sort buffer size at server startup:
[mysqld]
sort_buffer_size=512K
That sets the global value. A DBA with the SUPER privilege can change the global value
at runtime:
SET GLOBAL sort_buffer_size = 1024 * 256 ;
Each client that connects subsequently has its session variable initialized to the same
value, but can change the value as it likes. A client that performs large sorts might
increase the value:
SET SESSION sort_buffer_size = 1024 * 1024 ;
A SET statement that includes no GLOBAL or SESSION modifier changes the session value,
if there is one.
There is alternative syntax for writing system variable references:
SET @@ GLOBAL . var_name = value ;
SET @@ SESSION . var_name = value ;
The @@ syntax is more flexible. It can be used in statements other than SET , enabling you
to retrieve or examine individual system variables: