According to the GDPR
Article 5 of the GDPR states that personal data must be ‘kept in a form which permits identification of data subjects for no longer than is necessary for the purposes for which the personal data are processed.’
In other words, it is essential to set a retention period for your analytic data in line with the purposes specified to users.
Regarding AT Internet
If you wish to bring your procedure into compliance with regard to a limited retention period, we require that you attach a request on headed paper in an email to: firstname.lastname@example.org.
If you have already signed a DPA, the data storage duration has been specified in this document.
The description and impacts on your data are specified in the Customisation of Personal Data History under the ‘GDPR Compliance section of our Privacy Centre.