Oracle 参数 INMEMORY_AUTOMATIC_LEVEL 官方解释，作用，如何配置最优化建议
本站中文解释
INMEMORY_AUTOMATIC_LEVEL参数控制系统自动生成Oracle In-Memory可利用内存表后处理的内存负载水平。
该参数具有三个有效值：”DEFAULT”、”LOW”和”HIGH”。DEFAULT会根据表的容量调整自动内存负载。LOW 将会尽可能的将表放到内存中，即使表容量较大也不会弃掉任何表，而HIGH参数则是更多的表加入到In-Memory中，可能会导致压低表容量。
要正确设置INMEMORY_AUTOMATIC_LEVEL参数，首先应该分析应用程序使用的表，其容量大小。如果表容量不大，可以使用DEFAULT值，它会根据表大小自动进行调整。如果表容量较大，可以将参数设置为LOW或HIGH以增强应用程序性能。
官方英文解释
INMEMORY_AUTOMATIC_LEVEL is used to enable the Automatic In-Memory feature, which automates the management of the In-Memory Column Store (IM column store) to help ensure that the working data set is in the IM column store at all times.
| Property | Description |
|---|---|
|
Parameter type |
String |
|
Syntax |
|
|
Default value |
|
|
Modifiable |
|
|
Modifiable in a PDB |
Yes |
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Basic |
No |
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Oracle RAC |
All instances should use the same value. |
Typically, among all the IM enabled segments, only a subset is actively queried at any time. This subset is known as the working data set. The working data set is expected to change over time for many applications.
INMEMORY_AUTOMATIC_LEVEL attempts to keep the working data set in the IM column store at all times by moving segments in and out of the IM column store based on access patterns.
Oracle recommends that you provision enough memory for the working data set to fit in the IM column store.
The following values can be set:
-
LOW: The database evicts cold segments from the IM column store when it is under memory pressure. -
MEDIUM: The database evicts cold segments from the IM column store when it is under memory pressure. This level includes an additional optimization that ensures that any hot segment that was not populated because of memory pressure is populated first. -
HIGH: All segments in the database are enabled for the IM column store, except segments belonging to Oracle-maintained users and segments from external tables. Automatic In-Memory manages all segments enabled for the IM column store, keeping hot segments in the IM column store and evicting cold segments. This level includes an additional optimization that ensures that any hot segment that was not populated because of memory pressure is populated first. -
OFF: Automatic In-Memory is disabled. This value returns the IM column store to the behavior that existed prior to Oracle Database 18c, when the Automatic In-Memory features was introduced. If you do not expect a stable working data set, set the parameter toOFF. This is the default value.
See Also:
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Oracle Database Licensing
Information User Manual to learn which database offerings support the Automatic In-Memory feature -
Oracle Database In-Memory
Guide for more information about configuring the Automatic In-Memory feature
