Oracle TIMED_STATISTICS 参数 说明

MOS上有关TIMED_STATISTICS参数说明：

Init.ora Parameter "TIMED_STATISTICS" Reference Note [ID 30824.1]

Health CheckAlert: Consider setting TIMED_STATISTICS and STATISTICS_LEVEL to recommendedlevels [ID 957433.1]

Version	Parameter		Type	Modifiable
11.1.0.7	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
11.1.0.6	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
10.2.0.4	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
10.2.0.3	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
10.1.0.5	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
10.1.0.4	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
9.2.0.8	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
9.0.1.4	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)
8.1.7.4	timed_statistics	BOOLEAN	ALTER SESSION ALTER SYSTEM (IMMEDIATE)

TIMED_STATISTICSspecifies whether or not statistics related to time are collected. It isimportant to set TIMED_STATISTICS=TRUE for obtaining timing information whichwill help in tuning the database.

--TIMED_STATISTICS 指定是否收集于时间相关的统计信息，当设置为TURE时会获取有关时间的更多信息，从而帮助我们来优化DB.

有如下三种方法来设置该参数：

（1）初始化参数

The parameter can be set in theinitialisation file e.g.

timed_statistics= TRUE

（2）system 级别：

This parameter can be set at system levele.g.

ALTER SYSTEM SETtimed_statistics = TRUE

（3）session 级别：

This parameter can be set at session levele.g.

   ALTER SESSION SET timed_statistics = TRUE

When TIMED_STATISTICS is enabled statistics are generated for the following：

（1）PARSE, EXEC and FETCH CPU costs intrace files

（2）V$WAITSTAT

（3）V$FILESTAT and V$TEMPSTAT

（4）V$SYSSTAT and V$SESSTAT timedstatistics

Statistics affected by enabling TIMED_STATISTICS include

CPU used when call started

CPU used by this session

parse time cpu

parse time elapsed

redo write time

session connect time

Wait times arerecorded in V$SESSION_EVENT, V$SYSTEM_EVENT and V$SESSION_WAIT irrespective ofthe setting of TIMED_STATISTICS (9.2.0)

关于该参数的默认值，在官网上有关TIMED_STATISTICS 参数的说明：

http://docs.oracle.com/cd/E11882_01/server.112/e25513/initparams255.htm#REFRN10218

If STATISTICS_LEVEL is set to TYPICAL or ALL,then true

If STATISTICS_LEVEL is set to BASIC,then false

如果STATISTICS_LEVEL 设置为TYPICAL或者ALL,那么TIMED_STATISTICS 则默认为true。 如果STATISTICS_LEVEL设置为BASIC，则TIMED_STATISTICS 默认为false。

MOS上对STATISTICS_LEVEL的说明：

STATISTICS_LEVELspecifies the level of collection for the database and operating systemstatistics. The Oracle Database collects these statistics for a variety ofreasons, including making self-management decisions. Setting theSTATISTICS_LEVEL parameter to BASIC disables the collection of many importantstatistics required by Oracle Database features and functionality.STATISTICS_LEVEL=ALL should only be set for diagnostic purposes as required.

有关该参数在之前整理的Blog里有说明：

Oracle Statistic 统计信息 小结

http://blog.csdn.net/tianlesoftware/article/details/4668723

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