[Yandex Cloud documentation](../../../index.md) > [Yandex DataLens](../../index.md) > Troubleshooting > Backend app request timeout exceeded

# [Yandex DataLens] 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.

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.