What approach allows a data engineer to deduplicate records against previously processed records when inserting into a Delta table?

The approach of performing an insert-only merge with a matching condition on a unique key is effective for deduplicating records against previously processed records when inserting into a Delta table. This method leverages the capabilities of Delta Lake to apply transactional logic, specifically the merge operation, which allows you to specify conditions under which records should be inserted or updated.

By using a unique key as the matching condition, you can identify existing records in the Delta table that correspond to the incoming data. If a record with the same unique key already exists, you can choose to ignore the new incoming record (thereby avoiding duplication) or update the existing record based on your defined logic. This operation ensures that the data stays clean and avoids the pitfalls of duplicate entries.

This method is particularly robust because it does not just append new records blindly but instead provides intelligent handling based on the state of the table, which is crucial in environments where data may be modified or where historical integrity is vital.

In contrast, simply setting a configuration for deduplication would not provide the necessary control for decisions on individual records. VACUUM is a data management process that cleans up old versions and free space but doesn't handle deduplication during data insertion. Relying on schema enforcement alone does not address