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Parameter Sniffing – What is and How to deal with it

Antonios Chatzipavlis

Ένα από τα θέματα που σε κάποιες περιπτώσεις μας έχει ταλαιπωρήσει ιδιαίτερα αν δεν το γνωρίζουμε είναι το parameter sniffing.

Έχω κατά καιρούς διαβάσει και δει διάφορες προτάσεις για την αντιμετώπιση του.

Επειδή όμως δεν ήθελα απλά να το περιγράψω σε ένα ίσως μακροσκελές κείμενο αποφάσισα να το κάνω ένα web cast που ζωντανά δείχνω όλο το θέμα χωρίς slides αλλά με παραδείγματα.

Enjoy it.

 




Ο κώδικας του demo είναι

/*
    Parameter Sniffing Demo
    SQLSCHOOL GREECE
    V1 18/2/2013
*/

use AdventureWorks2012;
go

select * from Sales.SalesOrderDetail
where ProductID=897;
go

select * from Sales.SalesOrderDetail
where ProductID=870;
go


if OBJECT_ID(N'spGetOrdersByProductID') > 0 
    drop proc spGetOrdersByProductID
go

create proc spGetOrdersByProductID(@pid int)
as
    select * from Sales.SalesOrderDetail
    where ProductID=@pid;
go

/*
    Define the problem
*/
set statistics io on;
go

DBCC FREEPROCCACHE WITH NO_INFOMSGS;
GO

exec spGetOrdersByProductID 897;
go

exec spGetOrdersByProductID 870;
go


-- REVERSE ORDER

DBCC FREEPROCCACHE WITH NO_INFOMSGS;
GO

exec spGetOrdersByProductID 870;
go

exec spGetOrdersByProductID 897;
go

/* 
    Optimize for a typical parameter
*/

alter proc spGetOrdersByProductID (@pid int)
as
    select * from Sales.SalesOrderDetail
    where ProductID=@pid
    option (optimize for (@pid=897));
go

DBCC FREEPROCCACHE WITH NO_INFOMSGS;
GO

exec spGetOrdersByProductID 870;
go

exec spGetOrdersByProductID 897;
go

/*
    Optimize on every execution
*/

alter proc spGetOrdersByProductID (@pid int)
as
    select * from Sales.SalesOrderDetail
    where ProductID=@pid
    option (recompile);
go

DBCC FREEPROCCACHE WITH NO_INFOMSGS;
GO

exec spGetOrdersByProductID 870;
go

exec spGetOrdersByProductID 897;
go

/*
    Local Varibales and Optimize for Unknown
*/

alter proc spGetOrdersByProductID (@pid int)
as
    DECLARE @P INT = @pid;
    select * from Sales.SalesOrderDetail
    where ProductID=@p;
go

DBCC FREEPROCCACHE WITH NO_INFOMSGS;
GO

exec spGetOrdersByProductID 870;
go

exec spGetOrdersByProductID 897;
go


alter proc spGetOrdersByProductID (@pid int)
as
    select * from Sales.SalesOrderDetail
    where ProductID=@pid
    option (optimize for unknown);
go

DBCC FREEPROCCACHE WITH NO_INFOMSGS;
GO

exec spGetOrdersByProductID 870;
go

exec spGetOrdersByProductID 897;
go

Antonios Chatzipavlis

Antonios Chatzipavlis

Antonios is a Data Solutions Consultant and Trainer. He has been working in IT since 1988. In his career, he has worked as senior developer, IT Manager, Solutions Architect and IT Consultant. Since 1995 he has been devoted on new technologies and software development tools, mainly by Microsoft, either by training company staff and colleagues or assisting them in design, development and implementation as a consultant or chief developer. He has focused in Databases and Data Science since 1995. He specialized in Microsoft SQL Server since version 6.0 in areas like SQL Server Internals, Database Design and Development, Business Intelligence and in 2010 he has started working with Azure Data Platform, NoSQL databases, Big Data Technologies and Machine Learning. He is an active member of many IT communities in Greece, answering colleagues' questions and writing articles in his web site. He is the owner of SQLschool.gr which is a community portal with a lot of information about Microsoft SQL Server. He has been a Microsoft Certified Trainer (MCT) since 2000. Microsoft honored him as MVP on Data Platform due to his activities in SQL Server since 2010. He holds a large number of Microsoft Certifications and Microsoft SQL Server Certifications since version 6.5.


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