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On a large EF 4.0 model (700+ entities), we are getting poor performance on System.Data.Objects.ObjectContext.CreateObjectSet(string) . The call to this is triggered by a query like context.Users.FirstOrDefault(u => u.userId = 100) . The query performs well in general, but under load the query does not do well. We are running a 20 concurrent user load against a page that uses this query. The application for this page is under profiling mode i.e. we are using Visual Studio 2010 performance profiler while running this small load test. The profiler is using the "Sampling" mode. The application is built with ASP.NET 4.0 / ASP.NET MVC 3.0 and is hosted on IIS 7.5 on a Windows 7 server when the load test is being run. The profiling report shows a call stack that seems "infinite" i.e. there are a lot of calls to the below lines over and over. System.Data.Mapping.DefaultObjectMappingItemCollection.LoadObjectMapping System.Data.Mapping.DefaultObjectMappingItemCollection.LoadAssociationTypeMapping System.Data.Mapping.DefaultObjectMappingItemCollection.LoadObjectMapping System.Data.Mapping.DefaultObjectMappingItemCollection.LoadAssociationTypeMapping What could be the cause for poor performance and such infinite looking call stacks?

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