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canonical: en/troubleshooting/errors/ERR-DS_API-REQUEST_TIMEOUT.html
title: DataLens On-premises error ERR.DS_API.REQUEST_TIMEOUT
description: >-
  This page describes the Backend app request timeout exceeded DataLens
  On-premises error.
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# [DataLens On-premises] Backend app request timeout exceeded

`ERR.DS_API.REQUEST_TIMEOUT`

Request processing timeout expired.

Possible causes:

* It takes too long to process the request on the data source side.
* It takes too long to prepare the request to the data source on the DataLens side.

<!-- source: en/_includes/datalens/datalens-dataset-timeout-recommendations.md -->
To fix this error:

* Optimize the data in the source.
* Reduce the number of complex expressions with nested aggregations.
* Reduce the number of fields in the dataset.
* Create calculated fields at the dataset level instead of fields at the chart level.
<!-- endsource: en/_includes/datalens/datalens-dataset-timeout-recommendations.md -->