# DatabaseServiceImpl

This controller service provides an interface for one or more NiFi Ingest processors to communicate with an external database.

- IDOL NiFi Ingest Connectors keep a record of the items they have retrieved so that they do not need to synchronize those items again. Each time it synchronizes with your data repository, a NiFi Ingest Connector only retrieves new items, modified items, and information about the items that have been deleted. If you want to run an Apache NiFi cluster, you must configure your NiFi Ingest connectors to store their state information in an external database rather than in internal datastores.
- Some NiFi Ingest processors use a DocumentRegistryServiceImpl to ensure that indexing operations occur in the correct order. If you want to run an Apache NiFi cluster, you must configure your DocumentRegistryServiceImpl to store information in an external database.

For more information about how to set up the database service, see Create a Database Service.

## Properties

Name | Default Value | Description
--- | --- | ---
Connection String |  | The connection string to use to connect to the external database through ODBC.

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