Oracle 11g 自动任务

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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
---------------------------------------------------------------------------------------------------------------------------------

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
-------------------------------------------------------------------------------------------------------------

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
       ------------------------------ ---------------------------------------------------------------------------------------------------------------------------
       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.

1. 停用整个自动收集统计任务

exec dbms_auto_task_admin.disable( client_name=>’auto optimizer stats collection’,

operation => null,

window_name => null);

2. 只禁用星期一的自动任务（sys 用户登录），除了禁用 auto optimizer stats collection，还会禁用 automatic segment advisor 和 automatic sql tuning advisor

exec dbms_scheduler.disable( name => ‘MONDAY_WINDOW’,

force => TRUE);

SQL> select window_name, enabled from dba_scheduler_windows;

WINDOW_NAME                    ENABLED
       ------------------------------ ----------------------
       MONDAY_WINDOW                  FALSE
       TUESDAY_WINDOW                 TRUE
       WEDNESDAY_WINDOW               TRUE
       THURSDAY_WINDOW                TRUE
       FRIDAY_WINDOW                  TRUE
       SATURDAY_WINDOW                TRUE
       SUNDAY_WINDOW                  TRUE
       WEEKNIGHT_WINDOW               FALSE
       WEEKEND_WINDOW                 FALSE

9 rows selected.

3. 启用星期一自动任务

exec dbms_scheduler.enable( name => ‘MONDAY_WINDOW’);

4. 只禁用星期一的 auto optimizer stats collection 作业

exec dbms_auto_task_admin.disable( client_name => ‘auto optimizer stats collection’,

operation => null,

window_name => ‘MONDAY_WINDOW’);

SQL> select window_name,optimizer_stats,segment_advisor,sql_tune_advisor from dba_autotask_window_clients;

WINDOW_NAME                    OPTIMIZE_STATS      SEGMENT_ ADVISOR    SQL_TUNE_ADVISOR
       ------------------------------ -------- -------- -------------------------------------------------------------------------------
       MONDAY_WINDOW                  DISABLED                       ENABLED                     ENABLED
       TUESDAY_WINDOW                 ENABLED                        ENABLED                     ENABLED
       WEDNESDAY_WINDOW           ENABLED                        ENABLED                     ENABLED
       THURSDAY_WINDOW              ENABLED                        ENABLED                     ENABLED
       FRIDAY_WINDOW                    ENABLED                        ENABLED                     ENABLED
       SATURDAY_WINDOW              ENABLED                        ENABLED                     ENABLED
       SUNDAY_WINDOW                   ENABLED                        ENABLED                     ENABLED

7 rows selected.

5. 修改自动任务，必须先 disable，然后再 enable

例如，修改星期一自动任务的执行时间为晚上 11 点

exec dbms_scheduler.disable( name => ‘MONDAY_WINDOW’, force => TRUE);

exec dbms_scheduler.set_attribute( name => ‘MONDAY_WINDOW’, attribute => ‘repeat_interval’,

value => ‘freq=daily;byday=MON;byhour=23;byminute=0;bysecond=0’);

exec dbms_scheduler.enable( name => ‘MONDAY_WINDOW’);

6. 查看自动任务执行情况历史记录

SQL> select client_name, window_name, window_start_time, window_duration from dba_autotask_client_history where rownum < 5;

CLIENT_NAME                         WINDOW_NAME          WINDOW_START_TIME                                  WINDOW_DURATION
----------------------------------- -------------------- -------------------------------------------------- ---------------------------------------------------------------------------
auto optimizer stats collection     FRIDAY_WINDOW        24-OCT-14 11.10.54.202768 PM +08:00                +000000000 07:39:41.282770
auto optimizer stats collection     FRIDAY_WINDOW        07-NOV-14 10.00.00.099508 PM +08:00                +000000000 08:58:30.592880
auto optimizer stats collection     FRIDAY_WINDOW        14-NOV-14 10.00.00.091594 PM +08:00                +000000000 08:49:15.341343
auto optimizer stats collection     FRIDAY_WINDOW        21-NOV-14 10.00.00.076015 PM +08:00                +000000000 00:33:43.797989

7. 查看正在执行的自动任务

SQL> select client_name, JOB_SCHEDULER_STATUS from DBA_AUTOTASK_CLIENT_JOB;

参考：《基于 oracle 的 sql 优化》

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