2.153 INMEMORY_EXPRESSIONS_USAGE

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

INMEMORY_EXPRESSIONS_USAGE = { STATIC_ONLY | DYNAMIC_ONLY | ENABLE | DISABLE }

Default value

ENABLE

Modifiable

ALTER SYSTEM

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 named SYS_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 procedure DBMS_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: