Assume that you use Microsoft SQL Server 2012 or SQL Server 2014. Time taken by SQL Server to open the database post recovery would gradually increase when the number of files in the database or databases increases.
The issue occurs because there is inefficient code in the SQL Server startup phase when the number of databases or database or both files is large.
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To work around the issue, reduce the number of data files in the database.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.