The MySQL event scheduler is a thread that runs in the background looking for events to execute. It spends a lot of time sleeping -- and won't do anything unless the new global variable "event_scheduler" is set to ON (1). So if you want to take advantage of this feature, do the following:
SET GLOBAL event_scheduler = 1;
To turn the feature off, do:
SET GLOBAL event_scheduler = 0;
As with all "SET GLOBAL" statements, you need the SUPER privilege to change the setting of the event_scheduler variable.
It is also possible to start the server with:
mysqld ... --event_scheduler=1
You can see what the current state of affairs is with
SHOW VARIABLES LIKE 'event_scheduler';
or
SELECT @@event_scheduler;
Now let's look at the syntax for events.
一、前言
SET GLOBAL event_scheduler = 1;
---或我们可以在配置my.ini文件 中加上 event_scheduler = 1
SET GLOBAL event_scheduler = ON;
mysqld ... --event_scheduler=1
SHOW VARIABLES LIKE 'event_scheduler';
SELECT @@event_scheduler;
SHOW PROCESSLIST;
二、创建事件(CREATE EVENT)
CREATE EVENT [IF NOT EXISTS] event_name
ON SCHEDULE schedule
[ON COMPLETION [NOT] PRESERVE]
[ENABLE | DISABLE]
[COMMENT 'comment']
DO sql_statement;
schedule:
AT TIMESTAMP [+ INTERVAL INTERVAL]
| EVERY INTERVAL [STARTS TIMESTAMP] [ENDS TIMESTAMP]
INTERVAL:
quantity {YEAR | QUARTER | MONTH | DAY | HOUR | MINUTE |
WEEK | SECOND | YEAR_MONTH | DAY_HOUR | DAY_MINUTE |
DAY_SECOND | HOUR_MINUTE | HOUR_SECOND | MINUTE_SECOND}
USE test;
CREATE TABLE aaa (timeline TIMESTAMP);
CREATE EVENT e_test_insert
ON SCHEDULE EVERY 1 SECOND
DO INSERT INTO test.aaa VALUES (CURRENT_TIMESTAMP);
mysql> SELECT * FROM aaa;
+---------------------+
| timeline |
+---------------------+
| 2007-07-18 20:44:26 |
| 2007-07-18 20:44:27 |
| 2007-07-18 20:44:28 |
+---------------------+
CREATE EVENT e_test
ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 5 DAY
DO TRUNCATE TABLE test.aaa;
CREATE EVENT e_test
ON SCHEDULE AT TIMESTAMP '2007-07-20 12:00:00'
DO TRUNCATE TABLE test.aaa;
CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
DO TRUNCATE TABLE test.aaa;
CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
STARTS CURRENT_TIMESTAMP + INTERVAL 5 DAY
DO TRUNCATE TABLE test.aaa;
CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
ENDS CURRENT_TIMESTAMP + INTERVAL 5 DAY
DO TRUNCATE TABLE test.aaa;
CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
STARTS CURRENT_TIMESTAMP + INTERVAL 5 DAY
ENDS CURRENT_TIMESTAMP + INTERVAL 1 MONTH
DO TRUNCATE TABLE test.aaa;
8) 每天定时清空test表(只执行一次,任务完成后就终止该事件):
CREATE EVENT e_test
ON SCHEDULE EVERY 1 DAY
ON COMPLETION NOT PRESERVE
DO TRUNCATE TABLE test.aaa;
[COMMENT ‘comment’]可以给该事件加上注释。
三、修改事件(ALTER EVENT)
ALTER EVENT event_name
[ON SCHEDULE schedule]
[RENAME TO new_event_name]
[ON COMPLETION [NOT] PRESERVE]
[COMMENT 'comment']
[ENABLE | DISABLE]
[DO sql_statement]
ALTER EVENT e_test DISABLE;
ALTER EVENT e_test ENABLE;
ALTER EVENT e_test
ON SCHEDULE EVERY 5 DAY;
四、删除事件(DROP EVENT)
DROP EVENT [IF EXISTS] event_name
DROP EVENT e_test;
DROP EVENT IF EXISTS e_test;
注意:如果你将event执行了Alter event event_name disable.那么当你重新启动mysql服务
器后,该event将被删除(测试版本:5.1.30)
应用案例
- 首先创建存储过程
delimiter //
create procedure `Slave_Monitor`()
begin
SELECT VARIABLE_VALUE INTO @SLAVE_STATUS
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME='SLAVE_RUNNING';
IF ('ON' != @SLAVE_STATUS) THEN
SET GLOBAL SQL_SLAVE_SKIP_COUNTER=0;
SLAVE START;
END IF;
end; //
delimiter ;由于存储过程中无法调用类似 SHOW SLAVE STATUS 这样的语句,因此无法得到确切的复制错误信息和错误代码,不能进一步的处理 SLAVE 停止的各种情况。 - 接着,创建任务
CREATE EVENT IF NOT EXISTS `Slave_Monitor`
ON SCHEDULE EVERY 5 SECOND
ON COMPLETION PRESERVE
DO
CALL Slave_Monitor();
创建了一个任务,每 5秒钟执行一次,任务结束后依旧保留该任务,而不是删除。当然了,在本例中的任务不会结束,除非将它手动禁止了。 -
如果在运行中想要临时关闭一下某个任务,执行 ALTER EVENT 语句即可:
(root:localhost:)test> alter event `Slave_Monitor` ON
COMPLETION PRESERVE DISABLE;
(root:localhost:)test> alter event `Slave_Monitor` ON
COMPLETION PRESERVE ENABLE;