Executing stored proc from DotNet takes very long but in SSMS it is immediate

Question

I have a stored proc on SQL Server 2000 that takes 3 parameters. When I call the stored proc from DotNet using SqlCommand.ExecuteReader () it takes about 28 seconds.

When I run the same query inside SSMS directly it returns immediately.

When I take the query out of the stored proc and run it directly using DotNet it also returns immediately.

These are the results from a SQL Profiler session

SP Inside Dot Net

• Duration: 28030
• Reads: 2663365
• Writes: 0

SP Inside SSMS

• Duration: 450
• Reads: 23535
• Writes: 65

Query directly inside Dot Net

• Duration: 360
• Reads: 24865
• Writes: 57

The following things stand out to me:

• The stats for the SSMS and direct query in Dot Net are very similar
• The Dot Net SP one does a huge amount of reads but no writes
• The other two make very few reads, but a couple of writes

Any help would be appreciated.

Here is a slightly obviscated version of the SP:

I doubt that it is a query plan issue because even if I run it repeatedly from DotNet, I always get the same results.

Here is a version of the SP that's been altered slightly because of IP issues. I hope it still makes sense:

SELECT 
t1.pkiOrderID,
t1.fkiBasketId,
t1.sOriginBasketCode,
t1.dtDateCreated,
t1.sOrderCode,
t1.fkiUserCde,
t1.fkiOrgCde,
t1.sApprovalPerson,
t1.dtDateApproved,
t1.sRequestNo,
t1.dtRequiredDate,
t1.Requestor,
t1.OnBehalfOf,
t1.OrderDesc,
t1.OrderTypeId,
t1.fkiAgentID,
t1.fkiAgentRegionID,
stat.iStatus,
count(oi.pkiOrderItemId) as OrderItems,
count(wf.fkiOrderId) as WorkflowCount,
t1.Currency_Id,
t1.ExchangeRate,
t1.ref_odr_idn,
t2.sOrderCode as ref_odr_cde,
t1.ref_rfq_nbr,
t1.ref_rfs_nbr,
t1.ref_doc_nbr,
t1.ref_rsn,
t1.ref_forip_cde,
t1.ref_fa_nbr,
t1.odr_sub_typ
FROM    tbl1 t1 INNER JOIN 
tbl1Status stat ON
t1.pkiOrderID = stat.fkiOrderID AND
stat.dtDateStatusChanged = (SELECT MAX(stat2.dtDateStatusChanged) 
FROM tbl1Status stat2
WHERE stat2.fkiOrderId = t1.pkiOrderID) LEFT OUTER JOIN 
tbl1Item oi ON
t1.pkiOrderID = oi.fkiOrderId LEFT OUTER JOIN
tbl1Workflows wf ON
t1.pkiOrderID = wf.fkiOrderId LEFT OUTER JOIN 
tbl1 t2 ON 
t1.ref_odr_idn = t2.pkiOrderID
WHERE (t1.fkiUserCde = 'x'
or t1.fkiUserCde in (select fkiUserCde from tbl1 where fkiOrgCde in 
(select sys_org_cde from tbl3 t3 where t3.sys_lnk_org_cde = '123')))
AND ((t1.fkiOrgCde = '123'
and ('123' not in (select sys_org_cde from tbl3 t3) 
or (t1.OrderTypeID <     1 or stat.iStatus IN (2,3,4,5,6,7))))
OR (t1.fkiOrgCde in (select sys_org_cde from tbl3 t3 where     t3.sys_lnk_org_cde = '123')
and t1.OrderTypeID = 1 
and stat.iStatus NOT IN (2,3,4,5,6,7)))           
          AND   t1.OrderTypeID = 2

        GROUP BY
            t1.pkiOrderID,
            t1.fkiBasketId,
            t1.sOriginBasketCode,
            t1.dtDateCreated,
            t1.sOrderCode,
            t1.fkiUserCde,
            t1.fkiOrgCde,
            t1.sApprovalPerson,
            t1.dtDateApproved,
            t1.sRequestNo,
            t1.dtRequiredDate,
            t1.Requestor,
            t1.OnBehalfOf,
            t1.OrderDesc,
            t1.OrderTypeId,
            t1.fkiAgentID,
            t1.fkiAgentRegionID,
            stat.iStatus,
            t1.Currency_Id,
            t1.ExchangeRate,
            t1.ref_odr_idn,
            t2.sOrderCode,
            t1.ref_rfq_nbr,
            t1.ref_rfs_nbr,
            t1.ref_doc_nbr,
            t1.ref_rsn,
            t1.ref_forip_cde,
            t1.ref_fa_nbr,
            t1.odr_sub_typ
        ORDER BY t1.dtDateCreated DESC

Sorry about the formatting. I struggled to get it readable at all on the forum.

Answer 1

Just recreated the stored proc and that fixed it. Very strange indeed.

Answer 2

Since my comment seemed to provide the correct answer, I decided to move it into a full answer for posterity in the spirit of stackoverflow.

Your problem seems to be caused by SQL Server's Parameter Sniffing. To prevent it, just assign your incoming parameter values to other variables declared right at the top of your SP.

Example:

CREATE PROCEDURE dbo.MyProcedure
(
    @Param1 INT
)
AS

declare @MyParam1 INT
set @MyParam1 = @Param1

SELECT * FROM dbo.MyTable WHERE ColumnName = @MyParam1 

GO

I copied this information from eggheadcafe.com.