What is true when processing potential duplicate entries from an upstream system?

When processing potential duplicate entries from an upstream system, it is critical to understand how data is handled during the writing process. The correct answer indicates that each write will only contain unique records; however, it also acknowledges that newly written records may still have duplicates already present in the database.

This scenario arises because data ingestion from upstream systems can include duplicates, especially in environments where data is streamed or batched from multiple sources. While a deduplication process may be applied during the write operation to ensure that only unique records are committed in terms of what is being added, it does not inherently remove duplicates that might exist in the records already present in the destination. Therefore, it's possible that despite attempting to ensure uniqueness at the point of write, duplicates that were previously ingested remain after the new records have been added.

Understanding this is essential for data engineers as it informs them about the importance of using effective mechanisms for deduplication whether it be at the source, during transformation, or before final writes. This highlights the complexity of data management where multiple versions of records can co-exist and emphasizes the need for ongoing data quality checks post-ingestion.