SQL SERVER – DATABASE SCOPED CONFIGURATION – PARAMETER SNIFFING

Just a few hours ago, I finished my very last consulting engagement of the year Comprehensive Database Performance Health Check. My client had hired me after reading my recent series on Parameter Sniffing. In this blog post, we will discuss Database Scoped Configuration – Parameter Sniffing.

SQL SERVER - DATABASE SCOPED CONFIGURATION - PARAMETER SNIFFING scopedconfiguration0-800x263

Before continuing this blog post, I strongly suggest that you read the following blog posts to get an understanding of the background of the concept which I am going to discuss today.

Now the question is how we can get rid of the parameter sniffing at the entire server level. The answer is very simple if you are using SQL Server 2017 or 2019. The newer version of SQL Server can give you exactly the same behavior which you can get it by either using a local variable in the SP or using Optimize for Uknown query hint.

Let us see how you can do that with the help of Database Scoped Configuration – Parameter Sniffing.

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Database Scoped Configuration – Parameter Sniffing

There are two different ways to disable the traditional parameter sniffing. Let see both the methods.

Method 1: T-SQL

Run the following script for your database and disable parameter sniffing at the database level. Please replace the database name WideWorldImporters with your own database name.

USE [WideWorldImporters]
GO
ALTER DATABASE SCOPED CONFIGURATION
SET PARAMETER_SNIFFING = Off;
GO

Method 2: Via SSMS

Please see the following image which displays the database property. Over here you can disable the parameter sniffing.

SQL SERVER - DATABASE SCOPED CONFIGURATION - PARAMETER SNIFFING dbconfigoptimizeforuknown

Once you disable the parameter sniffing, create the following stored procedure.

-- Let us run the original stored procedure
CREATE OR ALTER PROC GetCustomerOrders (@CustomerID INT)
AS
SELECT *
FROM WideWorldImporters.Sales.Orders
WHERE CustomerID = @CustomerID
GO

Now enable the execution plan for your SSMS session and run the stored procedure with two different parameters.

-- Sample Stored Procedure
EXEC GetCustomerOrders 1060
EXEC GetCustomerOrders 90
GO

You can clearly notice from the execution plan that the execution plan does not sniff any particular parameter and executes the query at the average row count for statistics.

SQL SERVER - DATABASE SCOPED CONFIGURATION - PARAMETER SNIFFING scopedconfiguration

Once again, please note that this method removes the parameter sniffing but not necessarily fixes your performance issues. If you for sure want to properly estimate your row count, you can use recompilation. However, there are some negative stories associated with this method as well, I will share them some other time in the future.

Reference: Pinal Dave (https://blog.sqlauthority.com)

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1 Comment. Leave new

  • Thank Pinal for all four articles about PS (parameter sniffing). Now it is clear why PS happens and what are the options to avoid the performance issue. All provided solutions are trying to make SQL Server to not cache the execution plan.

    Now the question comes up that if caching execution plan cause PS issues and we are telling SQL Server to not cache execution plan, why SQL Server has the execution plan caching mechanism? Why Microsoft does not drop this feature?

    Reply

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