Question

I’ve a semi complex LINQ query that is running very slow. I do not believe it is using sub queries. I’ve tried to use logging and only see one query generated. the code is similar to the following:

dc.defferedloadingenabled = false
dc.objecttrackingenabled = false

dataloadoptions dlo = new dataloadoptions
dlo.loadwith<MyQuestion>(q => q.lotsofresponses)
dc.LoadOptions = dlo

IQuerayable<Question> questions = dc.questions.where( q => q.ParentId == specificID).orderBy(q => q.Rank);

foreach (question in questions)
{
}

Need help on how to speed this up. I believe I’m using the best practices.

Below is the SQL generated. I removed the actual key and column names. The count(*) looks odd to me.

SELECT [t0].[QId], [t0].[SId], [t0].[Tp], [t0].[St], [t0].[OL], [t0].[Is], [t0].[Tbl], [t0].[IsL], [t0].[Priority], [t1].[ResponseId], [t1].[QId] AS [QId2], [t1].[UId], [t1].[AN], [t1].[AT], (
    SELECT COUNT(*)
    FROM [dbo].[Responses] AS [t2]
    WHERE [t2].[QId] = [t0].[QId]
    ) AS [value]
FROM [dbo].[Questions] AS [t0]
LEFT OUTER JOIN [dbo].[Responses] AS [t1] ON [t1].[QuestionId] = [t0].[QuestionId]
WHERE [t0].[SurveyId] = @p0
ORDER BY [t0].[Priority], [t0].[QId], [t1].[ResponseId]

Answer 1

Since you’ve captured the query by logging, take it to SqlStudio and examine the execution plan.

• You should not see TableScan. If you see this, add a primary key to the table.
• You should not see ClusteredIndexScan on the LotsOfResponses table. If you see this, add an index on the foreign key column of the LotsOfResponses table.
• You should see ClusteredIndexSeek or IndexSeek on the Questions table. If you don’t see this, make Questions.ParentId into a Primary Key or add an index on it (whichever is most appropriate).

Also, run the query with

SET STATISTICS IO ON 
SET STATISTICS TIME ON

and check the messages tab for performance metrics.