Question

I have a query that uses nested CTEs which is in a user defined function. I have to use nested CTEs because I want to re-use some calculations/case statements from the previous selects. The query looks similar to what is below.

;with cte1 as 
(
   select a, b from Table1
),

ct2 as
(
   case when a =1 then 1 else 0 end as c, b from cte2
)
select * from cte2

I have this in a udf that is called from multiple stored procs. There are a large number of calculations being done inside this query. I’m noticing a performance difference when the query is run outside of the function. For around 12,000 records, it runs under 11 seconds when the query is run from the SQL management studio, applying all the parameters. When the same parameters are supplied to the udf, it takes around 55 seconds. I tried to put the query inside a stored proc instead of udf, but still the same 55 seconds. It looks like when the query is run from the management console, it uses parallelism for the query but not for function or stored proc.

This is not a major problem at this point but I would like to achieve the same 11 second performance if i can. Has anyone run into a similar scenario before?

Answer 1

display your “settings” from within the stored procedure and from just with SSMS. I have this same thing, faster in SSMS and slower in procedure. You can sometimes resolve this because SSMS is running with differeent settings than the procedure, get them same and you might be able to see the same performance in the procedure. Here is some example code to display the settings:

SELECT SESSIONPROPERTY ('ANSI_NULLS') --Specifies whether the SQL-92 compliant behavior of equals (=) and not equal to (<>) against null values is applied.
                                      --1 = ON 
                                      --0 = OFF

SELECT SESSIONPROPERTY ('ANSI_PADDING') --Controls the way the column stores values shorter than the defined size of the column, and the way the column stores values that have trailing blanks in character and binary data.
                                        --1 = ON 
                                        --0 = OFF

SELECT SESSIONPROPERTY ('ANSI_WARNINGS') --Specifies whether the SQL-92 standard behavior of raising error messages or warnings for certain conditions, including divide-by-zero and arithmetic overflow, is applied.
                                         --1 = ON 
                                         --0 = OFF

SELECT SESSIONPROPERTY ('ARITHABORT') -- Determines whether a query is ended when an overflow or a divide-by-zero error occurs during query execution.
                                      --1 = ON 
                                      --0 = OFF

SELECT SESSIONPROPERTY ('CONCAT_NULL_YIELDS_NULL') --Controls whether concatenation results are treated as null or empty string values.
                                                    --1 = ON 
                                                    --0 = OFF

SELECT SESSIONPROPERTY ('NUMERIC_ROUNDABORT') --Specifies whether error messages and warnings are generated when rounding in an expression causes a loss of precision.
                                              --1 = ON 
                                              --0 = OFF

SELECT SESSIONPROPERTY ('QUOTED_IDENTIFIER') --Specifies whether SQL-92 rules about how to use quotation marks to delimit identifiers and literal strings are to be followed.
                                             --1 = ON 
                                             --0 = OFF

you can just add them to your result set::

SELECT
    col1, col2
        ,SESSIONPROPERTY ('ARITHABORT') AS ARITHABORT
        ,SESSIONPROPERTY ('ANSI_WARNINGS') AS ANSI_WARNINGS
        ,SESSIONPROPERTY ('...
    FROM ...

if you ry them one at a time, try ARITHABORT first.

see: Resolving an ADO timeout issue in VB6
and Why would SET ARITHABORT ON dramatically speed up a query?