Weighted Baseline Regression Pattern for Query Store
Plan regression in SQL Server usually shows up quietly. A query that has been stable for a long time suddenly becomes slower, even though there were no deployments, schema changes, or obvious infrastructure problems. In many cases, the issue is tied to an execution plan change caused by statistics updates, parameter sensitivity, changing data distribution, or normal optimizer behavior.
Problem
A common starting point is comparing "yesterday vs today" using average duration. While quick, this approach often does not reflect the full behavior of the workload