Summary

From the set of regressed workloads that the SQL Database Engine team has handled over the years, the initial scenarios covered by QTA and CE Feedback are some of the most common after a database compatibility level upgrade (and, therefore, a CE upgrade), which can make users question whether to upgrade. But that is just because when upgrading from an old version, such as SQL Server 2008 or 2012, our T-SQL queries were fully tuned to the only CE model set that existed at the time. When some aspects of cardinality estimation changed, there was a possibility that some queries would have to be tuned for the new models. Fortunately, the SQL Database Engine team believes that backward compatibility is an asset in the SQL Database Engine and included these hints, which allow selective tuning opportunities for the scenarios covered by QTA and CE Feedback, as well as others less common not covered by QTA nor CE Feedback.

Whether you choose to use QTA or not, following the recommended...