statistics_level 參數的應用

 statistics_level 參數的應用

statistics_level參數是oracle9.2開始引入的一個控制系統統計參數收集的一個開關.一共有三個值:basic,typical,all.支持alter session,alter system 動態修改.如果要用statspack或者AWR收集系統性能統計數據.那麼這個參數的值必須爲typical或all.通常all是一個全面收集,包括OS以及sql執行路徑方面的一些統計信息,除非遇見非常嚴重的性能問題或在一些特殊的性能掙斷方面纔會用到statistics_level=all,平常statistics_level=typeical已經足夠掙斷99%的性能問題了.

example: seting statistics_level

 

alter system set statistics_level=basic;

alter system set statistics_level=typical;

alter system set statistics_level=all;

or

alter session set statistics_level=basic;

alter session set statistics_level=typical;

alter session set statistics_level=all;

 

oracle 還提供了v$statistics_level視圖用來記錄各個參數下oracle可以收集的統計信息的類別:

 

SQL> ALTER SYSTEM SET statistics_level=basic;

 

System altered.

 

SQL> SELECT statistics_name,

2         session_status,

3         system_status,

4         activation_level,

5         session_settable

6 FROM   v$statistics_level

7 ORDER BY statistics_name;

 

                               Session    System     Activation Session

Statistics Name                Status     Status     Level      Settable

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

Buffer Cache Advice            DISABLED   DISABLED   TYPICAL    NO

MTTR Advice                    DISABLED   DISABLED   TYPICAL    NO

PGA Advice                     DISABLED   DISABLED   TYPICAL    NO

Plan Execution Statistics      DISABLED   DISABLED   ALL        YES

Segment Level Statistics       DISABLED   DISABLED   TYPICAL    NO

Shared Pool Advice             DISABLED   DISABLED   TYPICAL    NO

Timed OS Statistics            DISABLED   DISABLED   ALL        YES

Timed Statistics               DISABLED   DISABLED   TYPICAL    YES

 

8 rows selected.

 

statistics_level=basic的情況下,oracle關閉了所有性能數據的收集,也就是如果要關閉AWR或statspack收集,只要設置alter system set statistics_level=basic;就行了;

 

SQL> ALTER SYSTEM SET statistics_level=typical;

 

System altered.

 

SQL> SELECT statistics_name,

2         session_status,

3         system_status,

4         activation_level,

5         session_settable

6 FROM   v$statistics_level

7 ORDER BY statistics_name;

 

                               Session    System     Activation Session

Statistics Name                Status     Status     Level      Settable

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

Buffer Cache Advice            ENABLED    ENABLED    TYPICAL    NO

MTTR Advice                    ENABLED    ENABLED    TYPICAL    NO

PGA Advice                     ENABLED    ENABLED    TYPICAL    NO

Plan Execution Statistics      DISABLED   DISABLED   ALL        YES

Segment Level Statistics       ENABLED    ENABLED    TYPICAL    NO

Shared Pool Advice             ENABLED    ENABLED    TYPICAL    NO

Timed OS Statistics            DISABLED   DISABLED   ALL        YES

Timed Statistics               ENABLED    ENABLED    TYPICAL    YES

 

8 rows selected.

 

statistics_level=typical的時候,除了plan_executetion_statistics和OS Statistics不能收集外,其他的都可以收集,如要要收集這個兩項,必須設置statistics_level=all;

 

SQL> ALTER SYSTEM SET statistics_level=all;

 

System altered.

 

SQL> SELECT statistics_name,

2         session_status,

3         system_status,

4         activation_level,

5         session_settable

6 FROM   v$statistics_level

7 ORDER BY statistics_name;

 

                               Session    System     Activation Session

Statistics Name                Status     Status     Level      Settable

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

Buffer Cache Advice            ENABLED    ENABLED    TYPICAL    NO

MTTR Advice                    ENABLED    ENABLED    TYPICAL    NO

PGA Advice                     ENABLED    ENABLED    TYPICAL    NO

Plan Execution Statistics      ENABLED    ENABLED    ALL        YES

Segment Level Statistics       ENABLED    ENABLED    TYPICAL    NO

Shared Pool Advice             ENABLED    ENABLED    TYPICAL    NO

Timed OS Statistics            ENABLED    ENABLED    ALL        YES

Timed Statistics               ENABLED    ENABLED    TYPICAL    YES

 

如果當statistics_level=ALL,系統收集所有的統計信息.