Question

I just launched my tiny webapp on my humble dedicated server (Win2003)… running ASP.NET MVC, LINQ2SQL, SQL Express 2005, and IIS6 (setup with wildcard mapping)

The website runs smoothly 90% of the times. However, on relatively high traffic, LINQ2SQL throws the error: Specified cast is not valid

This error is ONLY thrown at high traffic. I have NO IDEA how or exactly why this happens. Caching did not remove this problem entirely.

Anyone seen this problem before? are there any secret SQL Server tweaking I should’ve done? Or at least, any ideas on how to diagnose this issue? because i’m out!

Naimi

Stacktrace (from Event Log):

 at System.Data.SqlClient.SqlBuffer.get_SqlGuid()    at System.Data.SqlClient.SqlDataReader.GetGuid(Int32 i)    at Read_Friend(ObjectMaterializer`1 )    at System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext()    at Dudlers.Web.Models.DudlersDataContext.GetFriendRequests(Guid userId) in C:\Web\Models\DudlersDataContext.cs:line 562    at Dudlers.Web.Controllers.BaseController.View(String viewName, String masterName, Object viewData) in C:\Web\Controllers\BaseController.cs:line 39    at System.Web.Mvc.Controller.View(String viewName)    at Dudlers.Web.Controllers.CatController.Index() in C:\Web\Controllers\CatController.cs:line 25    at lambda_method(ExecutionScope , ControllerBase , Object[] )    at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)    at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(MethodInfo methodInfo, IDictionary`2 parameters)    at System.Web.Mvc.ControllerActionInvoker.c__DisplayClassb.b__8()    at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)    at System.Web.Mvc.ControllerActionInvoker.c__DisplayClassb.c__DisplayClassd.b__a()    at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(MethodInfo methodInfo, IDictionary`2 parameters, IList`1 filters)    at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)    at System.Web.Mvc.Controller.ExecuteCore()    at System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext)    at System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext)    at System.Web.Mvc.MvcHandler.ProcessRequest(HttpContextBase httpContext)    at System.Web.Mvc.MvcHandler.ProcessRequest(HttpContext httpContext)    at System.Web.Mvc.MvcHandler.System.Web.IHttpHandler.ProcessRequest(HttpContext httpContext)    at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()    at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) 

Answer 1

We had a similar problem with LINQ that we get ‘Unable to cast object of type ‘System.Int32’ to type ‘System.String” and ‘Specified cast is not valid.’

Examples of stacktraces

System.InvalidCastException: Unable to cast object of type 'System.Int32' to type 'System.String'.    at System.Data.SqlClient.SqlBuffer.get_String()    at System.Data.SqlClient.SqlDataReader.GetString(Int32 i)    at Read_Person(ObjectMaterializer`1 )    at System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext()    at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)    at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)    at RF.Ias.Services.Person.BusinessLogic.PersonTransactionScripts.GetPersons(IEnumerable`1 personIds, Boolean includeAddress, Boolean includeContact)    at CompositionAopProxy_5b0727341ad64f29b816c1b73d11dd44.GetPersons(IEnumerable`1 personIds, Boolean includeAddress, Boolean includeContact)    at RF.Ias.Services.Person.ServiceImplementation.PersonService.GetPersons(GetPersonRequest request)   System.InvalidCastException: Specified cast is not valid.    at System.Data.SqlClient.SqlBuffer.get_Int32()    at System.Data.SqlClient.SqlDataReader.GetInt32(Int32 i)    at Read_GetRolesForOrganisationResult(ObjectMaterializer`1 )    at System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext()    at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)    at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)    at RF.Ias.Services.Role.DataAccess.RoleDataAccess.GetRolesForOrganisation(GetRolesForOrganisationCriteria criteria, Int32 pageIndex, Int32 pageSize, Int32& recordCount)    at RF.Ias.Services.Role.BusinessLogic.RoleTransactionScripts.GetRolesForOrganisation(GetRolesForOrganisationCriteria criteria, Int32 pageIndex, Int32 pageSize, Int32& recordCount)    at CompositionAopProxy_4bd29c6074f54d10a2c09bd4ab27ca66.GetRolesForOrganisation(GetRolesForOrganisationCriteria criteria, Int32 pageIndex, Int32 pageSize, Int32& recordCount)    at RF.Ias.Services.Role.ServiceImplementation.RoleService.GetRolesForOrganisation(GetRolesForOrganisationRequest request) 

We used to get these exceptions if we first got a exception like this ‘System.InvalidOperationException: There is already an open DataReader associated with this Command which must be closed first.’ or ‘ A transport-level error has occurred when receiving results from the server. (provider: TCP Provider, error: 0 – An existing connection was forcibly closed by the remote host.)’.

The first exception occur for a different instance of the DataCOntext then for all those that then are following.

After some research and asking in this thread , I found that the reason was that I did not dispose the DataContexts. After I started to do that, it dissappered.