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 | |
| 11.1.0.6 | timed_statistics | BOOLEAN | ALTER SESSION | |
| 10.2.0.4 | timed_statistics | BOOLEAN | ALTER SESSION | |
| 10.2.0.3 | timed_statistics | BOOLEAN | ALTER SESSION | |
| 10.1.0.5 | timed_statistics | BOOLEAN | ALTER SESSION | |
| 10.1.0.4 | timed_statistics | BOOLEAN | ALTER SESSION | |
| 9.2.0.8 | timed_statistics | BOOLEAN | ALTER SESSION | |
| 9.0.1.4 | timed_statistics | BOOLEAN | ALTER SESSION | |
| 8.1.7.4 | timed_statistics | BOOLEAN | ALTER SESSION |
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$SESSTAT timedstatistics
Statistics affected by enabling TIMED_STATISTICS include
|
Wait times arerecorded in V$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://www.cndba.cn/Dave/article/1595
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