SQL Clone
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


Different execution plan between SQL and SP


Different execution plan between SQL and SP

Author
Message
SGT_squeequal
SGT_squeequal
SSC-Addicted
SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)

Group: General Forum Members
Points: 472 Visits: 1069
Hello, wonder if someone can help, i am looking at a performance issue with a stored procedure (SP). The SP its self is very simple only a few table joins and a single parameter ( integer data type).
When I execute as a stored procedure I get a totally different execution plan to when I execute as a select statement. Both queries are executed using the same method through SSMS QA
Below is an extract from statistics profiles, set one is from the SQL query, the corresponding execution plan to this query uses clustered index seeks whereas the second set of data executing as SP, you can see there are a lot of index scans. However, if i execute the SP as Exec SP_NAME PARAMETER with Recompile the query executes using the better execution plan.
AS SQL Query
Parent PhysicalOp LogicalOp
0 NULL NULL
1 Nested Loops Inner Join
2 Compute Scalar Compute Scalar
3 Nested Loops Inner Join
4 Nested Loops Inner Join
5 Nested Loops Inner Join
6 Compute Scalar Compute Scalar
7 Nested Loops Inner Join
8 Nested Loops Inner Join
9 Clustered Index Seek Clustered Index Seek
9 Filter Filter
11 Clustered Index Seek Clustered Index Seek
8 Clustered Index Seek Clustered Index Seek
6 Clustered Index Seek Clustered Index Seek
5 Clustered Index Seek Clustered Index Seek
4 Clustered Index Seek Clustered Index Seek
2 Clustered Index Seek Clustered Index Seek

AS SP
Parent PhysicalOp LogicalOp
0 NULL NULL
1 Sort Sort
2 Parallelism Gather Streams
3 Filter Filter
4 Hash Match Right Outer Join
5 Parallelism Repartition Streams
6 Index Scan Index Scan
5 Hash Match Inner Join
8 Bitmap Bitmap Create
9 Parallelism Repartition Streams
10 Hash Match Inner Join
11 Parallelism Repartition Streams
12 Clustered Index Scan Clustered Index Scan
11 Hash Match Inner Join
14 Parallelism Repartition Streams
15 Clustered Index Scan Clustered Index Scan
14 Parallelism Repartition Streams
17 Hash Match Inner Join
18 Compute Scalar Compute Scalar
19 Parallelism Repartition Streams
20 Clustered Index Scan Clustered Index Scan
18 Parallelism Repartition Streams
25 Index Scan Index Scan
8 Hash Match Inner Join
30 Bitmap Bitmap Create
31 Parallelism Repartition Streams
32 Index Scan Index Scan
30 Compute Scalar Compute Scalar
36 Parallelism Repartition Streams
37 Clustered Index Scan Clustered Index Scan


I have updated the statistics and added in a second variable inside the SP advice i have used in passed for parameter sniffing. Anyone come across this before and can anyone help shed some light on what is happening.


Cheers

*************************************************************

The first is always the hardestw00t
GilaMonster
GilaMonster
SSC Guru
SSC Guru (88K reputation)SSC Guru (88K reputation)SSC Guru (88K reputation)SSC Guru (88K reputation)SSC Guru (88K reputation)SSC Guru (88K reputation)SSC Guru (88K reputation)SSC Guru (88K reputation)

Group: General Forum Members
Points: 88779 Visits: 45284
Can you post the graphical plans please?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass


SGT_squeequal
SGT_squeequal
SSC-Addicted
SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)

Group: General Forum Members
Points: 472 Visits: 1069
HI Gail,




here you go thank you for you help, am tearing my hair out to try understand this Smile

*************************************************************

The first is always the hardestw00t
Attachments
SP_PLAN.sqlplan (19 views, 89.00 KB)
SELECT_PLAN.sqlplan (12 views, 44.00 KB)
SQLSACT
SQLSACT
SSCrazy
SSCrazy (2.1K reputation)SSCrazy (2.1K reputation)SSCrazy (2.1K reputation)SSCrazy (2.1K reputation)SSCrazy (2.1K reputation)SSCrazy (2.1K reputation)SSCrazy (2.1K reputation)SSCrazy (2.1K reputation)

Group: General Forum Members
Points: 2106 Visits: 2931
Im no Guru but I think this could be Bad Parameter Sniffing

http://sqlinthewild.co.za/index.php/2007/11/27/parameter-sniffing/
Dave Ballantyne
Dave Ballantyne
SSCrazy
SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)

Group: General Forum Members
Points: 2958 Visits: 8370
Hmm,

There is a slight difference in the code , the 'fast' version includes the extra clause @pJobId > 0
The optimizer is probably promoting this to the JobWorkJob.JobOID which give a differenting plan.

FROM
JobStay
JOIN UDStay ON JobStay.JobOID = UDStay.StayOID
JOIN Job ON JobStay.JobOID = Job.JobOID
JOIN Item ON JobStay.ItemOID = Item.ItemOID
LEFT JOIN JobWorkJob ON JobWorkJob.ForJobOID = JobStay.JobOID
LEFT JOIN JOB WJ ON WJ.JobOID = JobWorkJob.JobOID
JOIN Commodity ON Commodity.CommodityOID = Item.CommodityOID
JOIN UDCommodity ON UDCommodity.CommodityOID = Commodity.CommodityOID




WHERE
@pJobOID > 0
AND

JobWorkJob.JobOID = @pJobOID




However.....

Is this really what you want to do ?
You are left joining to JobWorkJob and then filtering the result!
Should that be an inner join ?
Or an outer join ON ID and ID and JobOID = @pJobOID



Clear Sky SQL
My Blog
SGT_squeequal
SGT_squeequal
SSC-Addicted
SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)

Group: General Forum Members
Points: 472 Visits: 1069
HI,

thanks for your reply but i took that extra parameter @joboid>0 out of the SP as its was a usless parameter not sure what the reason behind the person who wrote it putting it in.

*************************************************************

The first is always the hardestw00t
Dave Ballantyne
Dave Ballantyne
SSCrazy
SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)

Group: General Forum Members
Points: 2958 Visits: 8370
Maybe useless to you Smile but the optimizer is chosing to do something different because of it.

What about the outer join ? Is that what is intended ?



Clear Sky SQL
My Blog
SGT_squeequal
SGT_squeequal
SSC-Addicted
SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)

Group: General Forum Members
Points: 472 Visits: 1069
I have changed the joins now to inner joins as i realize the where clause negates on of the left joins and the other can also be inner join, not sure why they wrote this like it does i have a few more things to try with the parameter sniffing will give them a go Smile

*************************************************************

The first is always the hardestw00t
Dave Ballantyne
Dave Ballantyne
SSCrazy
SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)SSCrazy (3K reputation)

Group: General Forum Members
Points: 2958 Visits: 8370
So after you change it to an inner join , are you still getting different plans ?



Clear Sky SQL
My Blog
SGT_squeequal
SGT_squeequal
SSC-Addicted
SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)SSC-Addicted (472 reputation)

Group: General Forum Members
Points: 472 Visits: 1069
Yup i still have the same issue

if i run the SP like

Exec SP_NAME parameter_value with recompile

the SP run fine and uses the good execution plan

if i run it with

Exec SP_NAME parameter_value

it uses the poor execution plan

If i add the option to recompile within the SP and execute

Exec SP_NAME parameter_value

then i still get the poor execution plan w00t

Done a few changes to the SP to use local variables to try stop any parameter sniffing, no joy, tired the option (optimize for Unknown ) and still no joy Sad

*************************************************************

The first is always the hardestw00t
Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum

































































































































































SQLServerCentral


Search