Are there tools to capture query cost in dev and test environment?

Question

Are there tools to capture query cost in dev and test environment?

Toby Harman

SSCarpal Tunnel

Points: 4168
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March 20, 2011 at 4:50 pm

#157490

So I am trying to work out a way to ensure that the SQL development is performance checked at the most rudimentary levels.
I have this idea that if the test environment had a sufficiently sensible data set, I could review the stored procedures that are being generated and check each query's cost (or at least the estimated cost).
It was then suggested to me that this test could be automated and there might be a way to interrogate some meta-data about the cost of some queries. This data is all available through SHOWPLAN.
Has anyone come across this data or a tool to review it?

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Jeff Moden SSC Guru Points: 1004402 More actions · Answer 1

The supposed cost of a query frequently has nothing to do with its actual performance. Your best bet is to setup SQL Profiler to monitor the real use of resourses.

Here is proof of what I say. Run the following with the Actual Execution Plan enabled. Notice that the first plan claims 0% of batch while the measured run times that are displayed tell of a totally different story.

/****************************************************************************************

Purpose:

This code demonstrates that the estimated and actual execution plans in SQL Server can

be 100% INCORRECT and that the execution plan should only be relied on to provide hints

as to what may be wrong with a query rather than an absolute indication. This code runs

in SQL Server 2005 only.

The code creates a temp table for 10 years worth of dates starting with 2000-01-01 using

two different methods. The first method uses a recursive CTE and the second method uses

a "Tally" table. The output of each method is directed to a "throw-away" variable to

take display delays out of the picture.

Please check both the actual and estimated execution plans and compare the % of batch.

Please see the following article on how to build a Tally table and how they can be used

to replace certain While Loops.

http://www.sqlservercentral.com/articles/T-SQL/62867/

****************************************************************************************/

SET NOCOUNT ON

--=======================================================================================

-- Recursive method shown by (Name with-held)

--=======================================================================================

PRINT '========== Recursive method =========='

--===== Turn on some performance counters ===============================================

SET STATISTICS IO ON

SET STATISTICS TIME ON

DECLARE @Bitbucket DATETIME --Holds display output so display times aren't measured.

--===== Execute the code being tested ===================================================

DECLARE @DateVal DATETIME

SET @DateVal = '2000-01-01'

;with mycte as

(

select @DateVal AS DateVal

union all

select DateVal + 1

from mycte

where DateVal + 1 < DATEADD(yy, 10, @DateVal)

)

select @Bitbucket = d.dateval

from mycte d

OPTION (MAXRECURSION 0)

--===== Turn off the performance counters and print a separator =========================

SET STATISTICS TIME OFF

SET STATISTICS IO OFF

PRINT REPLICATE('=',90)

GO

--=======================================================================================

-- Tally table method by Jeff Moden

--=======================================================================================

PRINT '========== Tally table method =========='

--===== Turn on some performance counters ===============================================

SET STATISTICS IO ON

SET STATISTICS TIME ON

DECLARE @Bitbucket DATETIME --Holds display output so display times aren't measured.

--===== Execute the code being tested ===================================================

DECLARE @StartDate AS DATETIME

SET @StartDate = '2000-01-01'

SELECT TOP (DATEDIFF(dd,@StartDate,DATEADD(yy,10,@StartDate)))

@Bitbucket = @StartDate-1+t.N

FROM dbo.Tally t

ORDER BY N

--===== Turn off the performance counters and print a separator =========================

SET STATISTICS TIME OFF

SET STATISTICS IO OFF

PRINT REPLICATE('=',90)

GO

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

Toby Harman SSCarpal Tunnel Points: 4168 More actions · Answer 2

Fair enough! I wasn't convinced this was a "good" approach.

So I'll turn this question around a little bit.

How do people quality check code pro-actively? What tools should we be using to ensure that the SQL statements aren't doing table scans on multi-million row tables?

Jeff Moden SSC Guru Points: 1004402 More actions · Answer 3

I certainly do use the execution plans to give me an idea of where potential trouble spots are concerned especially when it comes to index usage and possible many-to-many joins (I call them "accidental Cross Joins") by looking for fat arrows with rowcounts larger than any of the tables. During test runs, though, I have SQL Profiler turned on to monitor just the SPID I'm working from. Of course, you also need enough test data to ensure scalability.

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)