# DocumentRegistryServiceImpl

Manages and updates a document registry database, which provides a way to ensure that indexing operations occur in the correct order.

When a connector performs the synchronize fetch action it might find items that have been modified. To update the content in the IDOL index, it sends two documents to the ingestion server: one is an ingest-delete, to delete the document that is currently in the index, and the second is an ingest-add, to add a document with the new content. The document that represents the delete operation must be indexed into the IDOL Content component first. Otherwise, the new content is added and then deleted.

For more information about using this service, see Index Documents in the Correct Sequence.

## Properties

Name | Default Value | Description
--- | --- | ---
Database Service |  | A DatabaseServiceImpl to use to communicate with an external database. You must use an external database if you are running an Apache NiFi cluster.
Document registry directory |  | The location in which to store the database. If you are running an Apache NiFi cluster, set the property "Database Service" instead.

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