SQL SERVER – Parameter Sniffing and OPTION (RECOMPILE)

Today is the last blog post of the year 2019 and this is also a final blog post in the series of Parameter Sniffing which I have been writing. I strongly recommend that you read my earlier blog posts on this topic before you consider the option of recompile suggested in this blog post.

SQL SERVER - Parameter Sniffing and OPTION (RECOMPILE) recompile-800x1016

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.

Here is what we have learned so far. It is extremely easy to overcome the problem of parameter sniffing. However, it is extremely difficult to overcome the performance problem which is introduced due to the parameter sniffing issue. There is no sure solution to overcome the problem if your stored procedure has sniffed the parameter and used that to build the execution plan. It is quite possible that even though we use the average value due to statistics the performance problem has yet not resolved.

There is only one sure resolution of the performance issue if the SQL Server execution plan is building execution plan which is not efficient for the parameter passed and that is the Recompilation of the stored procedure at every single run with the query hint OPTION (RECOMPILE).

While many want to argue that this may be very bad advice, there are moments where it has been amazing advice as well. In SQL Server there is no right or wrong answer unless while using production we are facing the negative consequence of it. It is important to know how each feature works and with the same spirit let us see how option recompile can help us in certain situations.

OPTION (RECOMPILE)

First, let us create a stored procedure that contains the keyword OPTION (RECOMPILE).

CREATE OR ALTER PROC GetCustomerOrders (@CustomerID INT)
AS
SELECT *
FROM WideWorldImporters.Sales.Orders
WHERE CustomerID = @CustomerID
OPTION (RECOMPILE)

Now enable the execution plan for your query window in SQL Server Management Studio (SSMS).

Next, let us run the following two stored procedures with two different parameters.

EXEC GetCustomerOrders 1060
EXEC GetCustomerOrders 90
GO

When we see the execution plan of the queries you will notice that this time the execution plan has a correct estimation of the rows and accordingly the query is consuming the resources which are needed to optimize that particular execution plan.

When the query needs more resources, it takes more resources and when needed fewer resources, it uses appropriate resources. This is a great adjustment and SQL Server makes every single time when the stored procedure is executed.

SQL SERVER - Parameter Sniffing and OPTION (RECOMPILE) optionrecompile

Of course, there is an additional cost associated when this stored procedure has been executed every single time as it has to recompile. However, this is when exactly you will have to make a decision considering various different baseline what works for you – better execution plans or cached execution plan.

I do not prefer to recompile every single stored procedure but whenever I ended up in the situation where I see the cached execution plan is creating more problems than it solves.

If you disagree, you are welcome as well. I have personally experienced enough examples while working with Comprehensive Database Performance Health Check in my career that I have started to use this feature of recompilation when I see no other options to improve the query performance.

On this note, happy new year 2020!

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

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2 Comments. Leave new

  • One situation where OPTION(RECOMPILE) is almost always beneficial is where a query would massively benefit from a filtered index, but SQL isn’t using it because parameters.

    Reply
  • If I have 10 queries in a store procedure, do I have to add option recompile for each query or can I do mix and match?

    Reply

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