---
title: Temporary Data Extensions
slug: segment/temporary-data-extensions
docTags: 
createdAt: 2026-01-18T22:41:14.931Z
---

Temporary Data Extensions are intermediary tables automatically generated by Unaric Segment during specific operations. These Data Extensions are stored in SFMC within the DESelect folder.

## How it works

Temporary Data Extensions are internally generated in the following scenarios:

- **Running a [preview](docId\:AFVLoJMPg9lrvaBMVJrtl)**: When you preview a selection, Unaric Segment stores the preview results in a temporary Data Extension to ensure that the Target Data Extension remains unaffected. Once you run the selection after previewing, the temporary Data Extension is automatically deleted.

::Image[]{src="https://support.deselect.com/hc/article_attachments/4418810475025" size="70" width="978" height="354" isUploading="false" darkWidth="978" darkHeight="354" alt="Preview temporary Data Extensions" showCaption="false"}

- **Using [Prio Deduplication](docId\:VKR1reInYO3puLdkKdvoU)**: In this case, Unaric Segment creates two temporary Data Extensions. The first Data Extension runs the selection as usual, while the second applies the deduplication rules.

## Clean temporary Data Extensions

:::hint{type="info"}
Starting May 2025, all newly created selections are automatically subject to the retention policy. This ensures that all associated preview and de-duplication Data Extensions are automatically deleted, optimizing storage usage without requiring manual intervention.

For Data Extensions created before June 2025, this automated clean-up process does not apply. These pre-existing DEs must be manually deleted to free up storage space.
:::

All the temporary Data Extensions are stored under the **DESelect** folder in SFMC Data Extensions. Temporary Data Extensions generated during a preview are automatically deleted once you officially run the Selection. However, administrators can configure a Data Retention Policy to automatically delete older temporary Data Extensions and free up storage space.

To this end, best practices include:

:::hint{type="success"}
- Set the correct Data Retention Policy for temporary Data Extensions in the Admin Panel. In this way, the temporary Data Extensions will be automatically deleted after a selected period of time.
- Delete old Selections that you don't need, as it will delete the Temporary Data Extensions related to it.
- Clean up existing temporary Data Extensions, based on the **LastModifiedDate**. Older temporary Data Extensions have fewer chances of being in use, so you can start by deleting the older ones.
:::

:::hint{type="info"}
Even after deleting the Temporary Data Extensions, the Selections related to them will still be accessible and work perfectly.
:::