Hi group,
I have a select statement that if run against a 1 million record
database directly in query analyzer takes less than 1 second.
However, if I execute the select statement in a stored procedure
instead, calling the stored proc from query analyzer, then it takes
12-17 seconds.
Here is what I execute in Query Analyzer when bypassing the stored
procedure:
USE Verizon
GO
DECLARE @.phonenumber varchar(15)
SELECT @.phonenumber = '6317898493'
SELECT Source_Identifier,
BADD_Sequence_Number,
Record_Type,
BAID ,
Social_Security_Number ,
Billing_Name,
Billing_Address_1,
Billing_Address_2,
Billing_Address_3,
Billing_Address_4,
Service_Connection_Date,
Disconnect_Date,
Date_Final_Bill,
Behavior_Score,
Account_Group,
Diconnect_Reason,
Treatment_History,
Perm_Temp,
Balance_Due,
Regulated_Balance_Due,
Toll_Balance_Due,
Deregulated_Balance_Due,
Directory_Balance_Due,
Other_Category_Balance
FROM BadDebt
WHERE (Telephone_Number = @.phonenumber) OR (Telephone_Number_Redef =
@.phonenumber)
order by Service_Connection_Date desc
RETURN
GO
Here is what I execute in Query Analyzer when calling the stored
procedure:
DECLARE @.phonenumber varchar(15)
SELECT @.phonenumber = '6317898493'
EXEC Verizon.dbo.baddebt_phonelookup @.phonenumber
Here is the script that created the stored procedure itself:
CREATE PROCEDURE dbo.baddebt_phonelookup @.phonenumber varchar(15)
AS
SELECT Source_Identifier,
BADD_Sequence_Number,
Record_Type,
BAID ,
Social_Security_Number ,
Billing_Name,
Billing_Address_1,
Billing_Address_2,
Billing_Address_3,
Billing_Address_4,
Service_Connection_Date,
Disconnect_Date,
Date_Final_Bill,
Behavior_Score,
Account_Group,
Diconnect_Reason,
Treatment_History,
Perm_Temp,
Balance_Due,
Regulated_Balance_Due,
Toll_Balance_Due,
Deregulated_Balance_Due,
Directory_Balance_Due,
Other_Category_Balance
FROM BadDebt
WHERE (Telephone_Number = @.phonenumber) OR (Telephone_Number_Redef =
@.phonenumber)
order by Service_Connection_Date desc
RETURN
GO
Using SQL Profiler, I also have the execution trees for each of these
two different ways of running the same query.
Here is the Execution tree when running the whole query in the
analyzer, bypassing the stored procedure:
------------
Sort(ORDER BY:([BadDebt].[Service_Connection_Date] DESC))
|--Bookmark Lookup(BOOKMARK:([Bmk1000]),
OBJECT:([Verizon].[dbo].[BadDebt]))
|--Sort(DISTINCT ORDER BY:([Bmk1000] ASC))
|--Concatenation
|--Index
Seek(OBJECT:([Verizon].[dbo].[BadDebt].[Telephone_Index]),
SEEK:([BadDebt].[Telephone_Number]=[@.phonenumber]) ORDERED FORWARD)
|--Index
Seek(OBJECT:([Verizon].[dbo].[BadDebt].[Telephone_Redef_Index]),
SEEK:([BadDebt].[Telephone_Number_Redef]=[@.phonenumber]) ORDERED
FORWARD)
------------
Finally, here is the execution tree when calling the stored procedure:
------------
Sort(ORDER BY:([BadDebt].[Service_Connection_Date] DESC))
|--Filter(WHERE:([BadDebt].[Telephone_Number]=[@.phonenumber] OR
[BadDebt].[Telephone_Number_Redef]=[@.phonenumber]))
|--Compute Scalar(DEFINE:([BadDebt].[Telephone_Number_Redef]=substring(Convert([BadDebt].[Telephone_Number]),
1, 10)))
|--Table Scan(OBJECT:([Verizon].[dbo].[BadDebt]))
------------
Thanks for any help on my path to optimizing this query for our
production environment.
Regards,
Warren Wright
Scorex Development Teamwarren.wright@.us.scorex.com (Warren Wright) wrote in message news:<8497c269.0308051401.2e65bb80@.posting.google.com>...
> Hi group,
> I have a select statement that if run against a 1 million record
> database directly in query analyzer takes less than 1 second.
> However, if I execute the select statement in a stored procedure
> instead, calling the stored proc from query analyzer, then it takes
> 12-17 seconds.
<snip
One possible reason is parameter sniffing - see here:
http://groups.google.com/groups?sel...7&output=gplain
Simon|||sql@.hayes.ch (Simon Hayes) wrote in message news:<60cd0137.0308060118.46c12f2e@.posting.google.com>...
> One possible reason is parameter sniffing - see here:
> http://groups.google.com/groups?sel...7&output=gplain
> Simon
Wow. Thats a bit of an eye opener. It makes me wonder how best to
make sure a decent plan is chosen by SQL Server, and the answer seems
to be to make it recompile the stored procedure every time ?
or is there a way to make SQL simply use the index at all times? I'd
hate to spend a lot of time on my dev machine getting the stored
procedure to run correctly on a million record table, only to port it
to my production machine and have it take forever on the 33 million
record database because of some magically crafted execution plan :-)
Thanks,
Warren|||Here is something else that I don't understand. The stored procedure
I listed above compares a phone number that is passed in against a
Telephone_Number column that is 15 digits long, and against a computed
column (Telephone_Number_Redef), that is the left 10 digits of the
Telephone_Number column.
This is because sometimes our client passes in a 10 digit number, and
sometimes a 15 digit version that includes some check digits on the
end (Don't ask).
Anyway, in the execution plan for when the stored proc is executing, I
see the following:
----------
Sort(ORDER BY:([BadDebt].[Service_Connection_Date] DESC))
|--Filter(WHERE:([BadDebt].[Telephone_Number]=[@.phonenumber] OR
[BadDebt].[Telephone_Number_Redef]=[@.phonenumber]))
|--Compute Scalar(DEFINE:([BadDebt].[Telephone_Number_Redef]=substring(Convert([BadDebt].[Telephone_Number]),
1, 10)))
|--Table Scan(OBJECT:([Verizon].[dbo].[BadDebt]))
----------
It appears to be recomputing the Telephone_Number_Redef column values
on the fly, instead of using the values already present. The
Telephone_Number_Redef column is indexed specifically to allow that
second comparison in the WHERE statement to be a SARG, but it seems
this is being ignored.
Is it being ignored because SQL had already decided to do a table
scan, and so though it might as well speed things up by not scanning
both columns? or is SQL doing a table scan because it thinks it needs
to re-compute the values for Telephone_Number_Redef on the fly?
Argh.
Thanks,
Warren Wright
Scorex Development Team
Dallas|||More follow-up on this issue, to help you experts analyze what's going
on here.
I've spent the day trying various things, with no success. I tried
using hints to suggest that the index on Telephone_Number_Redef be
used, which results in an error stating the stored procedure couldn't
be executed due to an unworkable hint.
I've tried declaring a new variable in the stored proc with a value
set equal to the @.phonenumber input, so SQL couldn't optimize based on
the actual value being passed in.
I've tried changing the index for the computed column to be a
clustered index.
I only wish I could simply tell SQL to use the same execution plan it
uses when I run the query from the analyzer!! All problems would be
solved!
No matter what, if I run the query from query analyzer, the response
time is a few milliseconds. If I run the stored procedure, the
response time is at least 17 seconds due to a completely suboptimal
execution plan (where the Telephone_Number_Redef's index isn't used at
all).
Introducing the new version of the stored proc with the OR statement
that checks against the computed column as well bogs down the
production server, and results in timeouts and app errors for our
client.
Frustrated,
Warren|||[posted and mailed, please reply in news]
Warren Wright (warren.wright@.us.scorex.com) writes:
> Here is something else that I don't understand. The stored procedure
> I listed above compares a phone number that is passed in against a
> Telephone_Number column that is 15 digits long, and against a computed
> column (Telephone_Number_Redef), that is the left 10 digits of the
> Telephone_Number column.
Computed column? Which you have an index on? Aha!
While Bart's article on parameter sniffing is good reading it is not
the answer here. Index on computed columns (as well on views) can
only be used if these SET options are ON: ANSI_NULLS, QUOTED_IDENTIFIER,
ANSI_WARNINGS, ARITHABORT, ANSI_PADDING and CONCAT_NULLS_YIELDS_NULL.
And NUMERIC_ROUNDABORT be OFF.
The killer here is usually QUOTED_IDENTIFIER. That option, together
with ANSI_NULLS is saved with the procedure, so that the run-time
setting does not apply, but the setting saved with the procedure.
QUOTED_IDENTIFIER is ON by default with ODBC and OLE DB, as well
with Query Analyzer. But OSQL and Enterprise Manager turns it off.
So you need to make sure that the procedure is created with
QUOTED_IDENTIFIER on.
You can review the current setting with
select objectproperty(object_id('your_sp'), 'IsQuotedIdentOn')
--
Erland Sommarskog, SQL Server MVP, sommar@.algonet.se
Books Online for SQL Server SP3 at
http://www.microsoft.com/sql/techin.../2000/books.aspsql
