Oracle 11g 12C自动任务

Automated maintenance tasks are tasks that are started automatically at regular intervals to perform maintenance operations on the database. An example is a task that gathers statistics on schema objects for the query optimizer. Automated maintenance tasks run in maintenance windows, which are predefined time intervals that are intended to occur during a period of low system load. You can customize maintenance windows based on the resource usage patterns of your database, or disable certain default windows from running. You can also create your own maintenance windows.

oracle 数据库预先定义了自动任务的三个功能：

1. Automatic Optimizer Statistics Collection

对没有统计信息或者过时统计信息的数据库对象进行收集统计信息，用来提高 sql 执行效率

2. Automatic Segment Advisor

建议回收哪些段空间可以回收

3. Automatic SQL Tuning Advisor

检测高负载的 sql 语句性能，并建议如何进行调优

SQL> select client_name, task_name, operation_name, status from dba_autotask_task;

CLIENT_NAME TASK_NAME OPERATION_NAME STATUS

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sql tuning advisor AUTO_SQL_TUNING_PROG automatic sql tuning task ENABLED

auto optimizer stats collection gather_stats_prog auto optimizer stats job ENABLED

auto space advisor auto_space_advisor_prog auto space advisor job ENABLED

oracle 11g 进行自动收集统计信息的任务客户端名称为 auto optimizer stats collection，实际调用执行的是 gather_stats_prog 程序，而 gather_stats_prog 程序调用的是 dbms_stats.gather_database_stats_job_proc 存储过程。

SQL> select program_type, program_action, enabled from dba_scheduler_programs where program_name='GATHER_STATS_PROG';

PROGRAM_TYPE PROGRAM_ACTION ENABLED

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STORED_PROCEDURE dbms_stats.gather_database_stats_job_proc TRUE

oracle 11g 默认的任务执行时间：

1. 星期一至星期五晚上 10 点开始，执行 4 个小时

2. 星期六，星期日早上 6 点开始，执行 20 个小时

SQL> select window_name, repeat_interval, duration, enabled from dba_scheduler_windows where enabled='TRUE';

WINDOW_NAME REPEAT_INTERVAL DUATION ENABLED

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MONDAY_WINDOW freq=daily;byday=MON;byhour=22;byminute=0; bysecond=0 +000 04:00:00 TRUE

TUESDAY_WINDOW freq=daily;byday=TUE;byhour=22;byminute=0; bysecond=0 +000 04:00:00 TRUE

WEDNESDAY_WINDOW freq=daily;byday=WED;byhour=22;byminute=0; bysecond=0 +000 04:00:00 TRUE

THURSDAY_WINDOW freq=daily;byday=THU;byhour=22;byminute=0; bysecond=0 +000 04:00:00 TRUE

FRIDAY_WINDOW freq=daily;byday=FRI;byhour=22;byminute=0; bysecond=0 +000 04:00:00 TRUE

SATURDAY_WINDOW freq=daily;byday=SAT;byhour=6;byminute=0; bysecond=0 +000 20:00:00 TRUE

SUNDAY_WINDOW freq=daily;byday=SUN;byhour=6;byminute=0; bysecond=0 +000 20:00:00 TRUE

7 rows selected.