Set the auto_close database option to off
Applies to: 
SQL Server
This rule checks whether the AUTO_ CLOSE option is set OFF. When AUTO_CLOSE is set ON, this option can cause performance degradation on frequently accessed databases because of the increased overhead of opening and closing the database after each connection. AUTO_CLOSE also flushes the procedure cache after each connection.
Best practices recommendations
If a database is accessed frequently, set the AUTO_CLOSE option to OFF for the database.
For more information
ALTER DATABASE SET Options (Transact-SQL)