Oracle 12cR2
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https://docs.oracle.com/database/122/TDPPT/oracle-database-performance-method.htm#TDPPT007
Gathering Database Statistics Using the Automatic Workload Repository
Database statistics provide information about the type of load on the database and the internal and external resources used by the database. To accurately diagnose performance problems with the database using ADDM, statistics must be available.
A cumulative statistic is a count such as the number of block reads. Oracle Database generates many types of cumulative statistics for the system, sessions, and individual SQL statements. Oracle Database also tracks cumulative statistics about segments and services. Automatic Workload Repository (AWR) automates database statistics gathering by collecting, processing, and maintaining performance statistics for database problem detection and self-tuning purposes.
By default, the database gathers statistics every hour and creates an AWR snapshot, which is a set of data for a specific time that is used for performance comparisons. The delta values captured by the snapshot represent the changes for each statistic over the time period. Statistics gathered by AWR are queried from memory. The gathered data can be displayed in both reports and views.
--每小时收集一次AWR快照
The following initialization parameters are relevant for AWR:
--下面是两个和AWR相关的参数。
STATISTICS_LEVEL
Set this parameter to TYPICAL (default) or ALL to enable statistics gathering by AWR. Setting STATISTICS_LEVEL to BASIC disables many database features, including AWR, and is not recommended.
--设置以上参数为basic会禁用掉很多数据库特性，包括AWR，不建议设置basic
CONTROL_MANAGEMENT_PACK_ACCESS
Set to DIAGNOSTIC+TUNING (default) or DIAGNOSTIC to enable automatic database diagnostic monitoring. Setting CONTROL_MANAGEMENT_PACK_ACCESS to NONE disables many database features, including ADDM, and is strongly discouraged.
--关闭此参数会禁用掉很多数据库的特性，包括ADDM,不建议关闭。
SQL> show parameter statistics_level --默认值不需要修改
NAME TYPE VALUE
------------------------ ----------- ------------------------------
statistics_level string TYPICAL
SQL> show parameter control_management --默认值不需要修改
NAME TYPE VALUE
-------------------------------------- ----------- ------------------------------
control_management_pack_access string DIAGNOSTIC+TUNING
SQL>
以上大家知道我们收集到AWR信息是和那些参数有关，默认设置即可，不需要修改。
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