SQL Server Query Store: Why Performance History Matters

This article discusses the importance of SQL Server Query Store for diagnosing performance problems that are no longer active. It highlights how historical data on queries, execution plans, and runtime metrics allows DBAs to compare behavior during an incident window with normal periods. The author advises starting with the incident time, checking if affected queries became slower, if plans changed, or if execution frequency spiked. It cautions against jumping to conclusions about 'bad plans' without considering workload changes, parameter values, or resource pressure. The article is practical for IT professionals dealing with SQL Server performance tuning and troubleshooting.