seniorT-SQL
What is query plan regression and how do you fix it?
Updated May 17, 2026
Short answer
Plan regression occurs when a new execution plan performs worse than a previous one.
Deep explanation
Plan regression happens after schema changes, stats updates, or parameter shifts. SQL Server may choose a suboptimal plan due to changes in cardinality estimates or missing indexes. Query Store is commonly used to detect and force last good plans.
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