event_scheduler及集群定期清理表（DROP TEMPTABLE）的定时任务说明

在集群中，每个gcluster都存在一个user为event_scheduler的连接，如下：

Id        User        Host        db        Command        Time        State        Info 1        event_scheduler        localhost        NULL        Daemon        60428        Waiting for next activation        NULL

event_scheduler用户用于进行数据库执行计划的执行。
gbase集群的执行计划存储在gbase.event系统表中，查询该表可以看当前数据库定义的计划任务，默认如下：

gbase> select * from gbase.event \G
*************************** 1. row ***************************
                  db: gbase                                                           
                name: drop_temp_table                                                 
                body: DROP TEMPTABLE
             definer: root@localhost                                                               
          execute_at: NULL
      interval_value: 1
      interval_field: DAY
             created: 2015-01-30 10:07:34
            modified: 2015-01-30 10:07:34
       last_executed: 2015-03-23 02:07:34
              starts: 2015-01-30 02:07:34
                ends: NULL
              status: ENABLED
       on_completion: DROP
            sql_mode: ANSI_QUOTES,IGNORE_SPACE
             comment:                                                                 
          originator: 0
           time_zone: +08:00
character_set_client: utf8                            
collation_connection: utf8_general_ci                 
        db_collation: utf8_general_ci                 
           body_utf8: DROP TEMPTABLE
1 row in set (Elapsed: 00:00:00.00)

使用show create event event_name的方式可以查看计划任务的创建语句如下：

gbase> show create event drop_temp_table;
+-----------------+--------------------------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| Event           | sql_mode                 | time_zone | Create Event                                                                                                                            | character_set_client | collation_connection | Database Collation |
+-----------------+--------------------------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| drop_temp_table | ANSI_QUOTES,IGNORE_SPACE | +08:00    | CREATE EVENT "drop_temp_table" ON SCHEDULE EVERY 1 DAY STARTS '2015-01-30 10:07:34' ON COMPLETION NOT PRESERVE ENABLE DO DROP TEMPTABLE | utf8                 | utf8_general_ci      | utf8_general_ci    |
+-----------------+--------------------------+-----------+-----------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
1 row in set (Elapsed: 00:00:00.01)

关于临时表清理（DROP TEMPTABLE）任务描述：
每天定期执行一次临时表清理任务（如本例中每天02:07:34执行），执行的具体sql为：DROP TEMPTABLE;
可以手工执行sql的方式进行临时表的清理：

gbase> DROP TEMPTABLE;
Query OK, 0 rows affected (Elapsed: 00:00:19.48)