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# Configuring Cache Type and Size at the Descriptor Level

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The TopLink cache is an in-memory repository that stores recently read or written objects based on class and primary key values. TopLink uses the cache to do the following:

- improve performance by holding recently read or written objects and accessing them in-memory to minimize database access

- manage locking and isolation level

- manage object identity

Table: Descriptor Support for Identity Map summarizes which descriptors support identity map configuration.

Descriptor Support for Identity Map

Descriptor | Using TopLink Workbench | Using Java
--- | --- | ---
Relational DescriptorsFoot 1 |  |
Object-Relational Descriptors |  |
EIS DescriptorsFoot 2 |  |
XML Descriptors |  |

Footnote 1 Relational class descriptors only (see "Relational Class Descriptors").

Footnote 2 EIS root descriptors only (see "EIS Root Descriptors").

This configuration overrides the default identity map configuration defined at the project level (see "Configuring Cache Type and Size at the Project Level").

Note: If a descriptor is a child in an inheritance hierarchy, TopLink uses the cache type are size that you configure for the parent root descriptor. For more information about inheritance, see "Descriptors and Inheritance".

For detailed information on caching and object identity, and the recommended settings to maximize TopLink performance, see to "Cache Type and Object Identity".

For more information about the cache, see Understanding the Cache.