Cool Features of SQL Server 2014: Improved Cardinality Estimates
With all the cheerleading and the steady drumbeat of new features being released to Azure, it's easy to lose track of the many cool and valuable new features released in the on-premises version of SQL Server. One of the crown jewels of SQL Server, the cardinality estimator (CE), underwent a large redesign for SQL Server 2014 to improve performance. Cardinality estimates are an extremely important part of query processing. In a nutshell, cardinality estimates are what the relation engine predicts for the number of rows affected by a given operation, including intermediate row sets like those created by filters, aggregations, joins and spool.
Originally Posted May 14, 2015