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# Configuring Cache Existence Checking at the Descriptor Level

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When TopLink writes an object to the database, TopLink runs an existence check to determine whether to perform an insert or an update.

By default, TopLink checks against the cache. Oracle recommends that you use this default existence check option for most applications. Checking the database for existence can cause a performance bottleneck in your application.

Table: Descriptor Support for Existence Checking summarizes which descriptors support existence checking.

Descriptor Support for Existence Checking

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").

You can configure existence checking at the descriptor level to override the project level configuration (see "Configuring Existence Checking at the Project Level").

For more information see:

- "Cache Type and Object Identity"

- "Queries and the Cache"

- "Using Registration and Existence Checking"