Query runs in less than a millisecond in SQL, but times out in Entity Framework

Question

The following linq-to-entities query throws

Entity Framework Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.

after ToList()ing it.

 var q = (from contact 
          in cDB.Contacts.Where(x => x.Templategroepen.Any(z => z.Autonummer == templategroep.Autonummer) 
                                && !x.Uitschrijvings.Any(t => t.Templategroep.Autonummer == templategroep.Autonummer)) 
          select contact.Taal).Distinct();

((System.Data.Objects.ObjectQuery)q).ToTraceString() gives me:

SELECT 
[Distinct1].[Taal] AS [Taal]
FROM ( SELECT DISTINCT 
[Extent1].[Taal] AS [Taal]
FROM [dbo].[ContactSet] AS [Extent1]
WHERE ( EXISTS (SELECT 
1 AS [C1]
FROM [dbo].[TemplategroepContact] AS [Extent2]
WHERE ([Extent1].[Autonummer] = [Extent2].[Contacts_Autonummer]) AND ([Extent2].[Templategroepen_Autonummer] = @p__linq__0)
)) AND ( NOT EXISTS (SELECT 
1 AS [C1]
FROM [dbo].[UitschrijvingenSet] AS [Extent3]
WHERE ([Extent1].[Autonummer] = [Extent3].[Contact_Autonummer]) AND ([Extent3].[Templategroep_Autonummer] = @p__linq__1)
))
)  AS [Distinct1]

the query from tracestring runs in under 1 seconds in sql management studio, but times out when actually to-listing it? how is that possible again?

*Update: added SQL PROFILER output for query * this runs as slow as the EF ToList() (>30seconds)

exec sp_executesql N'SELECT 
[Distinct1].[Taal] AS [Taal]
FROM ( SELECT DISTINCT 
    [Extent1].[Taal] AS [Taal]
    FROM [dbo].[ContactSet] AS [Extent1]
    WHERE ( EXISTS (SELECT 
        1 AS [C1]
        FROM [dbo].[TemplategroepContact] AS [Extent2]
        WHERE ([Extent1].[Autonummer] = [Extent2].[Contacts_Autonummer]) AND ([Extent2].[Templategroepen_Autonummer] = @p__linq__0)
    )) AND ( NOT EXISTS (SELECT 
        1 AS [C1]
        FROM [dbo].[UitschrijvingenSet] AS [Extent3]
        WHERE ([Extent1].[Autonummer] = [Extent3].[Contact_Autonummer]) AND ([Extent3].[Templategroep_Autonummer] = @p__linq__1)
    ))
)  AS [Distinct1]',N'@p__linq__0 int,@p__linq__1 int',@p__linq__0=1,@p__linq__1=1

Answer 1

I observed this issue with EF6.

await _context.Database.SqlQuery<MyType>(sql) was timing out even when my timeout value was cranked up to 60 seconds. However, executing the exact same SQL (used profiler to confirm the sql I passed in was unmodified) in SSMS yielded expected results in one second.

exec sp_updatestats

Fixed the issue for me.

Answer 2

(DBCC FREEPROCCACHE)
DBCC DROPCLEANBUFFERS

made the problem go away for now, but I think that might just be a temp. solution

Answer 3

I know this is a little late, but I found the answer here.

Basically Entity Framework likes to track everything by default. If you don't need it (i.e. not inserting or updating or deleting entities), turn it off to speed up your queries.

If you're using Entity Framework Code First you can achieve this like so:

var q = (from contact
      in cDB.Contacts.AsNoTracking()
          .Where(x => x.Templategroepen.Any(z => z.Autonummer == templategroep.Autonummer) 
                            && !x.Uitschrijvings.Any(t => t.Templategroep.Autonummer == templategroep.Autonummer)) 
      select contact.Taal).Distinct();