Cardinality estimation feedback

As mentioned in Chapter 6, Understanding Statistics, the cardinality estimator estimates the number of rows to be processed by each operator in a query execution plan. Similar to the concept of memory grant feedback, and also based on the query store, cardinality estimation feedback is another intelligent query processing feature introduced with SQL Server 2022, which can learn and adjust based on the history of previous query executions. As we learned in Chapter 6, Understanding Statistics, the cardinality estimator uses different model assumptions to perform cardinality estimations. In addition, starting with SQL Server 2014, SQL Server has two different cardinality estimators to choose from.

The cardinality estimator feedback feature works by analyzing repeating queries. If an existing model assumption appears incorrect or produces a suboptimal query plan, the cardinality estimator will identify and use a model assumption that better fits a given...