Symptoms

Consider the following scenario:

  • You have a query that contains a predicate that involves a parameterized scalar user-defined function.

  • There are multiple combinations of input parameter values that may produce the same result by this user-defined function.

  • SQL Server uses the New Cardinality Estimator in which the database compatibility mode is set to 120.


In this scenario, when you run the query, you experience poor query performance because of an incorrectly estimated number of rows for the predicate that involves the user-defined function in the query plan.

Resolution

This problem was first fixed in the following cumulative update for SQL Server:

Cumulative Update 6 for SQL Server 2014 Service Pack 1

After you install this cumulative update package, you have to enable trace flag 4199. To do this, you can add the -T4199 startup parameter. Or, you can use the dbcc traceon(4199) statement for a specific session.

Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server:

Latest cumulative update for SQL Server 2014

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

References

Learn about the terminology Microsoft uses to describe software updates.

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