Question

Stored procedure slow from VB.NET, fast from SSMS

Asked by: gunman69

I have an SP that takes 23 parameters, and the result set depends (of course) on the parameters.
In this particular scenario (i.e. with a specific set of values for the parameters) the SP returns 30 000 rows, with around 150 columns.

When I run the SP directly from the query window in SSMS, the SP executes at around 50 secs (completely, with output result in the result window). The "Reads" columns in the profiles states 1927431 reads.
When I execute the SP from VB.NET, it now takes more than 20 minutes, and the "Reads" column states a much greater value (unfortunately I don't have right now, but it's at least 100 times greater).

In VB.NET, I call ExecuteReader. For testing purposes, I have removed the code that iterates over the IDataReader which is returned. In other words, I dont pull much data from SQL Server to the VB.NET process (or at least that's the way I think it works).

The VB.NET executable lives on the same machine as SQL Server, whereas SSMS and SQL Server are on different machines (separated with a slow network)

Note that I THINK that the call from VB.NET sometimes executes at around the same time as from within SSMS (under a minute). I am not sure, since I haven't worked with this code for long myself.

Any ideas what can cause the performance difference?

Perhaps I am completely wrong, but to me it looks like SQL Server picks different execution plans, when I perform the call from SSMS v.s. when I call from VB.NET. (Because of the big difference in number of reads).

Thanks!
/Fredrik

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Asked On
2009-11-06 at 06:28:59ID24877898
Tags

SQL Server 2005

,

VB.NET

,

stored procedure

,

performance

Topics

MS SQL Server

,

.NET

,

Visual Basic Programming

Participating Experts
3
Points
500
Comments
12

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Answers

 

by: aneeshattingalPosted on 2009-11-06 at 06:37:24ID: 25759423

can you paste the sp here , if you can change the sp to use dynamic sql it will perforrm better

 

by: gunman69Posted on 2009-11-06 at 07:20:42ID: 25759836

Nope, I can't share it due to policy reasons.

But in a general case, the SP performance itself isn't so much the problem (at least not when I execute it from within SSMS).

Why would dynamic SQL perform better?

/F

 

by: emoreauPosted on 2009-11-06 at 07:44:34ID: 25760056

 

by: acperkinsPosted on 2009-11-06 at 07:46:41ID: 25760077

>>In this particular scenario (i.e. with a specific set of values for the parameters) the SP returns 30 000 rows, with around 150 columns.<<
This is your problem.  Unless you are prepared to reduce the number of rows/columns, then you are SOL.

 

by: gunman69Posted on 2009-11-06 at 16:56:01ID: 25764423

acperkins: I agree that the amount of data being returned is large, but there isn't much I can do about it without modifying the client code and that is not feasable.

Still, 50 seconds is ok for our use of the SP (it runs in a batch over-night) but 20 minutes is not.

I still don't understand why it takes so much longer to run exactly the same SP from ADO.NET compared to running from SSMS. Also, I still don't know why dynamic SQL would help. And, not so important perhaps, I don't know what SOL means...

Thanks anyway,

Fredrik

 

by: gunman69Posted on 2009-11-06 at 16:59:13ID: 25764436

emoreau: Thanks for the link, interesting. I will try the work-around when I get a chance (Monday). I doubt it will help though, since when I run the same SP with the same values of the parameters from SSMS it is so much faster than from ADO.NET. To me, it doesn't look like that is the same problem described in the article. Can't hurt to try it, though.

/Fredrik

 

by: acperkinsPosted on 2009-11-06 at 17:18:02ID: 25764504

>> but there isn't much I can do about it without modifying the client code and that is not feasable.<<
It may not be feasable, but it is also not a good design and in general it is lousy to return so much data to the client.

>>Also, I still don't know why dynamic SQL would help<<
It won't.


Good luck.

 

by: aneeshattingalPosted on 2009-11-06 at 17:33:50ID: 25764562

how did u compute the time.. it can be the time for loading the data onto the datagrid

 

by: gunman69Posted on 2009-11-06 at 23:22:44ID: 25765298

emoreau: The times compared should be reasonably compatible. The code in VB.NET is basically this

- Start timer
- ExecuteReader
- Stop timer

And, since the ExecuteReader returns a forward-only cursor, I assume that the measured time is between the start of the SP to (approximately) the time the first row of data is available.

BTW, I am not loading the data into a datagrid, this is a non-visual application that analyses the data.

 

 

by: emoreauPosted on 2009-11-07 at 05:28:54ID: 25766238

>> between the start of the SP to (approximately) the time the first row of data is available

The ExecuteReader is a synchronous method. When the method completes you have all your data (and not only the first row).

 

by: gunman69Posted on 2009-11-07 at 08:33:57ID: 25766890

Actually, I don't think that is the way it works - the ExecuteReader represents a stream of data. When the client calls Next, data is pulled from SQL Server (with some buffering). That's why the reader's connection is not available for other operations until Close is called.

Anyway, it really doesn't matter. The time to execute AND return all data in SSMS is much less than the time to execute and return a fraction of the data.

 

 

by: gunman69Posted on 2009-11-09 at 23:48:50ID: 31651028

The problem was indeed a cached plan which, for some combinations of the values of the SP parameters, was very inefficient.

I added WITH RECOMPILE to the SP, which took the execution time from both SSMS and VB.NET down to ~40 seconds. The extra overhead of recompiling the SP each execution is minimal, about 10 ms.

20120131-EE-VQP-002

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