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Asked: 2026-05-18T03:58:04+00:00

I have an issue with a linq to sql query – performance wise. What

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I have an issue with a linq to sql query – performance wise.
What i am trying to do, is find out if the elements of my collection of about 500 items (in a List) match db entries. Currently, this operation alone is taking about 300 seconds to complete! The database contains over a million rows and is bound to grow in the future so this level of performance so early on is simply unacceptable. Sample below:

var query = from item in db.DataTable.Where(x => x.date == suppliedDate)
            where inputList.Contains(item.name)
            select new { item.name};

Help!

edit:
Thanks a lot for all your suggstions! i just wanted to add a few additional observations as i’ve now been able to view the SQL output of my LINQ query (see below)

SELECT [t0].[name]
FROM [dw].[DataTable] AS [t0]
WHERE ([t0].[name] IN (@p0, @p1, @p2, @p3, @p4, @p5, @p6, @p7, @p8, @p9, @p10, @p11, @p12, @p13, @p14, @p15, @p16, @p17)) AND ([t0].[date] = @p18)
-- @p0: Input NVarChar (Size = 5; Prec = 0; Scale = 0) [Mark]
-- @p1: Input NVarChar (Size = 5; Prec = 0; Scale = 0) [Owen]
-- @p2: Input NVarChar (Size = 5; Prec = 0; Scale = 0) [James]
-- @p3: Input NVarChar (Size = 5; Prec = 0; Scale = 0) [John]

etc..

Is this making 500 separate hits on the DB? (As Ian suggested)? and is there any way i can imporve performance without having to resort to stored procedures or creating an additional table? (both options not really available to me right now). I’ve tried Geoff’s suggestion and this brought my run time from 300 seconds to about 126 seconds – but that’s still a lot especially considering how a db join would take less than 10 seconds at most.

Many Thanks

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1 Answer

  1. Editorial Team
    -- @p0: Input NVarChar (Size = 5; Prec = 0; Scale = 0) [Mark]

    Is the column varchar?

    If you check the execution plan for that query, you might see sql server converting the whole index to nvarchar (DOOOOOM!)

    The fix is to convert the parameters to varchar.

    You can get the command and reset the types of the parameters on it directly (to ansi-string in your case).

    http://msdn.microsoft.com/en-us/library/system.data.linq.datacontext.getcommand.aspx
    http://msdn.microsoft.com/en-us/library/system.data.dbtype.aspx

    Then you might call ExecuteReader on that command, yielding a DbDataReader. You can hand this DbDataReader to the Translate method of your datacontext, and it will give you the IEnumerable<T> that you’d expect from linq.

    http://msdn.microsoft.com/en-us/library/bb534213.aspx

    I’ve posted the code to accomplish this, here

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