Oracle 参数 INMEMORY_EXPRESSIONS_USAGE 官方解释，作用，如何配置最优化建议
本站中文解释
Oracle提供了INMEMORY_EXPRESSIONS_USAGE参数，它可以控制可以存储在Oracle In-Memory表中的表达式的量。该参数允许在表进入In-Memory存储之前，将表达式添加到查询性能优化中以实现动态缓存。
INMEMORY_EXPRESSIONS_USAGE参数可以设置为两个值–FORCE和AUTOMATIC。
当参数设置为FORCE时，表空间中的所有表达式都将添加到表的索引缓存中，以便在运行时将查询性能优化操作应用于表。
当参数设置为AUTOMATIC时，Oracle In-Memory会将表的表达式添加到缓存中，并自动优化Oracle表的性能。此参数对于具有非常复杂的查询语句的数据库尤其有用。
因此，要正确设置INMEMORY_EXPRESSIONS_USAGE参数，请首先根据系统需求来确定要在In-Memory表中存储的表达式的数量，然后根据实际情况设置参数。如果需要确保In-Memory表中存储索引大量表达式，请使用FORCE参数，而如果不需要添加大量表达式，可以使用AUTOMATIC参数自动优化Oracle表。
官方英文解释
INMEMORY_EXPRESSIONS_USAGE controls which In-Memory Expressions (IM expressions) are populated into the In-Memory Column Store (IM column store) and are available for queries.
| Property | Description |
|---|---|
|
Parameter type |
String |
|
Syntax |
|
|
Default value |
|
|
Modifiable |
|
|
Modifiable in a PDB |
Yes |
|
Basic |
No |
|
Oracle RAC |
The same value must be used on all instances. |
The four values for this parameter are:
-
STATIC_ONLY: Tables enabled for in-memory and containing certain data types such as Oracle numbers or JSON will have these columns populated in the IM column store using a more efficient representation. Note that this setting will increase the in-memory footprint for some tables. A static configuration enables the IM column store to cache OSON (binary JSON) columns, which are marked with an IS_JSON check constraint. Internally, an OSON column is a hidden virtual column namedSYS_IME_OSON. In contrast, a dynamic configuration automatically creates and populates frequently used expressions. -
DYNAMIC_ONLY: IM expressions will be automatically created and populated into the IM column store, if used in conjunction with PL/SQL procedureDBMS_INMEMORY.IME_CAPTURE_EXPRESSIONS. Note that setting this value will increase the in-memory footprint for some tables. -
ENABLE: Both static and dynamic IM expressions will be populated into the IM column store and available to be used by queries. Note that setting this value will increase the in-memory footprint for some tables. This is the default value. -
DISABLE: No IM expressions of any kind will be populated into the IM column store.
Changing the mode of a parameter does not have an immediate effect on existing in-memory data. For example, if the inmemory_expressions_usage clause is changed from DYNAMIC_ONLY to DISABLE, the stored IM expressions are not immediately removed. The next repopulation will not bring back the expressions in memory, thereby effectively removing the expressions.
See Also:
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“INMEMORY_VIRTUAL_COLUMNS”
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Oracle Database In-Memory
Guide for more information about IM expressions - Oracle Database PL/SQL
Packages and Types Reference for more information about theDBMS_INMEMORYPL/SQL package
