How To Use Parameters Like a Pro
And Boost Performance
Guy Glantser
SQL Saturday Sydney
18th February 2017
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Let’s Begin
with a Story…
What is Parameterization?
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Why is it So Important?
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When does it Become
Problematic?
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How can we Deal with it?
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The “Customers by Country” Case Study
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The “Customers by Country” Case Study
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Case Study
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Plan Caching
Query plans are cached in the plan
cache in order to be reused and
avoid the cost of recompiling the
same queries again and again.
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Plan Caching
Plan Caching
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7 Ways To Execute Your Query
7 Ways…
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Parameter Sniffing
The query optimizer “sniffs” the
parameter values during first
execution, and optimizes the query
based on these values.
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Parameter Sniffing
Local variables are not parameters,
so the query optimizer has nothing
to sniff.
The values of local variables are
only assigned at run-time.
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Parameter Sniffing
Is Parameter Sniffing
Good or Bad?
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Parameter Sniffing
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Parameter Sniffing
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Parameter Sniffing
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Parameter Sniffing
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Parameter
Sniffing
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Non-Uniform Data Distribution
Possible Solutions:
• sys.sp_recompile
• WITH RECOMPILE
• OPTION (RECOMPILE)
• OPTION (OPTIMIZE FOR)
• Multiple Stored Procedures
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Changing Parameter Values
The optimizer sniffs the parameter
values at compile-time, so if you
change the parameter values at
run-time, the plan will not be
suitable for the new values.
Changing
Parameter
Values
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Simple vs. Forced Parameterization
In simple parameterization, the
optimizer automatically parameterizes
only simple plans, in which the
parameter values have absolutely no
effect on the plan chosen.
Simple vs. Forced Parameterization
In forced parameterization, the
optimizer automatically parameterizes
most plans.
Simple vs. Forced Parameterization
Parameterization can be applied at the:
Database Level
Query Template Level
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Simple vs.
Forced
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Summary
Parameterization is a very important
aspect of the query processor’s job
when compiling and executing
queries.
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Summary
Inappropriate handling of
parameterization can lead to
poor performance.
Unfortunately, it is common to
neglect this area.
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Summary
Tip #1
Usually, data distribution is
more or less uniform, so, in
general, prefer parameterized
queries over non-parameterized
queries.
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Summary
Tip #2
When data is not uniformly
distributed, rewrite your code
using one of the methods
shown in this session.
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Summary
Tip #3
Avoid the use of local variables
as an alternative for
parameters.
Use parameters instead.
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Summary
Tip #4
Don’t change parameter values
inside your stored procedures.
Pass the calculated values to
inner stored procedures to use
parameter sniffing or use
OPTION (RECOMPILE).
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Summary
Tip #5
Force parameterization only
when you have no other choice.
Prefer forced parameterization
at the query template level.
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Back to the Story…
My Blog Series About Parameterization…
http://www.madeiradata.com/tag/parameterization-series/
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Questions?
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Name:
Email Address:
Twitter:
Blog:
Podcast:
Guy Glantser
[email protected]
@guy_glantser
www.madeiradata.com/author/guy
www.sqlserverradio.com
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