Events are executed by a special event
scheduler thread; when we refer to the Event Scheduler,
we actually refer to this thread. When running, the event
scheduler thread and its current state can be seen by users having
PROCESS privilege in the output
SHOW PROCESSLIST, as shown in
the discussion that follows.
variable determines whether the Event Scheduler is enabled and
running on the server. It has one of these 3 values, which affect
event scheduling as described here:
OFF: The Event Scheduler is stopped. The event scheduler thread does not run, is not shown in the output of
SHOW PROCESSLIST, and no scheduled events are executed.
OFFis the default value for
ON: The Event Scheduler is started; the event scheduler thread runs and executes all scheduled events.
When the Event Scheduler is
ON, the event scheduler thread is listed in the output of
SHOW PROCESSLISTas a daemon process, and its state is represented as shown here:
mysql> SHOW PROCESSLIST\G *************************** 1. row *************************** Id: 1 User: root Host: localhost db: NULL Command: Query Time: 0 State: NULL Info: show processlist *************************** 2. row *************************** Id: 2 User: event_scheduler Host: localhost db: NULL Command: Daemon Time: 3 State: Waiting for next activation Info: NULL 2 rows in set (0.00 sec)
Event scheduling can be stopped by setting the value of
DISABLED: This value renders the Event Scheduler nonoperational. When the Event Scheduler is
DISABLED, the event scheduler thread does not run (and so does not appear in the output of
SHOW PROCESSLIST). In addition, the Event Scheduler state cannot be changed at runtime.
If the Event Scheduler status has not been set to
event_scheduler can be toggled
is also possible to use
ON when setting this variable. Thus, any of the
following 4 statements can be used in the mysql
client to turn on the Event Scheduler:
SET GLOBAL event_scheduler = ON; SET @@global.event_scheduler = ON; SET GLOBAL event_scheduler = 1; SET @@global.event_scheduler = 1;
Similarly, any of these 4 statements can be used to turn off the Event Scheduler:
SET GLOBAL event_scheduler = OFF; SET @@global.event_scheduler = OFF; SET GLOBAL event_scheduler = 0; SET @@global.event_scheduler = 0;
numeric equivalents, the value displayed for
VARIABLES is always one of
DISABLED has no numeric
equivalent. For this reason,
OFF are usually preferred over
0 when setting this
Attempting to set
without specifying it as a global variable causes an error:
mysql< SET @@event_scheduler = OFF; ERROR 1229 (HY000): Variable 'event_scheduler' is a GLOBAL variable and should be set with SET GLOBAL
It is possible to set the Event Scheduler to
DISABLED only at server startup. If
OFF, you cannot set
DISABLED at runtime. Also, if the Event
Scheduler is set to
DISABLED at startup, you
cannot change the value of
event_scheduler at runtime.
To disable the event scheduler, use one of the following two methods:
As a command-line option when starting the server:
In the server configuration file (
my.inion Windows systems), include the line where it will be read by the server (for example, in a
To enable the Event Scheduler, restart the server without the
command-line option, or after removing or commenting out the line
in the server configuration file, as appropriate. Alternatively,
you can use
0) in place of the
DISABLED value when starting the server.
You can issue event-manipulation statements when
event_scheduler is set to
DISABLED. No warnings or errors are generated
in such cases (provided that the statements are themselves
valid). However, scheduled events cannot execute until this
variable is set to
1). Once this has been done, the event
scheduler thread executes all events whose scheduling conditions
Starting the MySQL server with the
--skip-grant-tables option causes
event_scheduler to be set to
DISABLED, overriding any other value set either
on the command line or in the
my.ini file (Bug #26807).
For SQL statements used to create, alter, and drop events, see Section 20.4.3, “Event Syntax”.
MySQL provides an
EVENTS table in the
INFORMATION_SCHEMA database. This table can be
queried to obtain information about scheduled events which have
been defined on the server. See Section 20.4.4, “Event Metadata”,
and Section 21.7, “The INFORMATION_SCHEMA EVENTS Table”, for more information.
For information regarding event scheduling and the MySQL privilege system, see Section 20.4.6, “The Event Scheduler and MySQL Privileges”.