Entity Framework SQL Timeout after x number of WCF requests - sql

Question

There are around 300 clients each making requests to a WCF service every ten minutes. They are not all making requests at exactly the same time.
This LINQ query in a Service class is trying to get configFeedItems that the client has not already received (note: I'm using Ninject to inject the Repository into my Service class):
var configFeedItems = (from feedItem in configFeedItemRepository.All
where feedItem.Id > lastReceivedFeedItemId &&
(feedItem.TargetUserId == userId || feedItem.TargetUserId == null) &&
!feedItem.ConfigFeedItemReceipts.Any(x => x.User.Id == userId)
select feedItem)
.ToList();
Which causes this exception to be thrown:
[SqlException (0x80131904): Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.]
This is the SQL that gets generated:
exec sp_executesql N'SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Action] AS [Action],
[Extent1].[TargetId] AS [TargetId],
[Extent1].[TargetCommand] AS [TargetCommand],
[Extent1].[CreatedOn] AS [CreatedOn],
[Extent1].[TargetUserId] AS [TargetUserId],
[Extent1].[ChannelToUpdate] AS [ChannelToUpdate],
[Extent1].[CreatedBy_Id] AS [CreatedBy_Id]
FROM [dbo].[ConfigFeedItem] AS [Extent1]
WHERE ([Extent1].[Id] > #p__linq__0) AND ([Extent1].[TargetUserId] = #p__linq__1 OR [Extent1].[TargetUserId] IS NULL) AND ( NOT EXISTS (SELECT
1 AS [C1]
FROM [dbo].[ConfigFeedItemReceipt] AS [Extent2]
WHERE ([Extent1].[Id] = [Extent2].[ConfigFeedItem_Id]) AND ([Extent2].[User_Id] = #p__linq__2)))',N'#p__linq__0 int,#p__linq__1 uniqueidentifier,#p__linq__2 uniqueidentifier',#p__linq__0=0,#p__linq__1='E3D4044F-497E-4EEC-890C-021F72826505',#p__linq__2='E3D4044F-497E-4EEC-890C-021F72826505'
If I stop and restart the AppPool in IIS, it's fine for about five minutes and then it happens again.
If I change the LINQ query so it's not pulling in the ConfigFeedItemReceipts, I don't get any timeout.
It only seems to happen when I try to query the child collection.
I've tried using joins instead and EF generates a query with a simple LEFT OUTER JOIN but I still get a timeout.
It's like there is a lock or something or the connections are maxed out.
I tried SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED; before executing the LINQ query but this didn't make a difference
Any ideas what is causing the SQL timeout?
UPDATE: not all requests cause a timeout, some work some don't even though it's the same query.

Answer 1

I assume that you're using sql server with code first approach. If so, try to change the default command timeout value during initiating the instance of dbcontext as stated below. Your db operations might take longer than the default timeout.
public class YourContext : DbContext
{
public YourContext()
: base("YourConnectionStringName")
{
((IObjectContextAdapter)this).ObjectContext.CommandTimeout = 300;
}
}