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Materialized views data purge

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Applies to: ✅ Microsoft Fabric ✅ Azure Data Explorer

Note

This article provides steps about how to delete personal data from the device or service and can be used to support your obligations under the GDPR. For general information about GDPR, see the GDPR section of the Microsoft Trust Center and the GDPR section of the Service Trust portal.

Data purge commands can be used to purge records from materialized views. The same guidelines for purging records from a table apply to materialized views purge.

The purge command only deletes records from the materialized part of the view (what is the materialized part?). Therefore, if the source table of the materialized view includes records to purge, these records may be returned from the materialized view query, even after purge completed successfully.

The recommended process for purging records from a materialized view is:

  1. Purge the source table of the materialized view.
  2. After the source table purge is completed successfully, purge the materialized view.

Warning

Data deletion through the .purge command is designed to be used to protect personal data and should not be used in other scenarios. It is not designed to support frequent delete requests, or deletion of massive quantities of data, and may have a significant performance impact on the service.

Note

While purge is running on a materialized view, materialization is not run. In this scenario, the materialization process is disabled because it conflicts with the purge process, both trying to work on the same extents (data shards). The purge process is always prioritized over the materialization process. If the purge takes a long while to complete, the materialized view might start lagging. We recommend that you only query the materialized part of the view during this time. For more information, see how materialized views work.

Limitations

The purge predicate of a materialized view purge can only reference the group by keys of the aggregation, or any column in a arg_max()/arg_min() /take_any() view. It cannot reference other aggregation functions result columns.

For example, for a materialized view MV, which is defined with the following aggregation function:

T | summarize count(), avg(Duration) by UserId

The following purge predicate isn't valid, since it references the result of the avg() aggregation:

MV | where avg_Duration > 1h

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