v.23.10Improvement

Setting apply_deleted_mask for Debugging Deleted Rows in ClickHouse

The setting apply_deleted_mask when disabled allows to read rows that where marked as deleted by lightweight DELETE queries. This is useful for debugging. #55952 (Alexander Gololobov).
Introduced the apply_deleted_mask setting that controls whether rows marked as deleted by lightweight DELETE queries are filtered out during reads.

Why it matters

This feature allows users to disable the deletion mask, enabling the reading of rows that have been logically deleted. It is useful for debugging and inspecting data that would normally be hidden by DELETE operations.

How to use it

Set the apply_deleted_mask setting to 0 (false) to disable applying the deletion mask and allow reading deleted rows. By default, this setting is enabled to exclude deleted rows.