Automatic statistics updating
The database server updates statistics automatically according to a predefined schedule and a set of expiration policies. The Auto Update Statistics (AUS) maintenance system identifies tables and indexes that require new optimizer statistics and runs the appropriate UPDATE STATISTICS statements to optimize query performance.
The AUS maintenance system updates the statistics for tables that are in logged databases, regardless of the database locale. By making current table statistics available to the query optimizer, the AUS maintenance system can reduce the risk of performance degradation from inefficient query plans.
Depending on your system, you might need to adjust the AUS expiration policies or schedule. The AUS maintenance system resides in the sysadmin database.