WCF reliability issues

Question

Trying to test the reliability of my wcf services. I am calling a wcf service within a loop from the client side. The wcf rest service (webhttpbinding) does some data processing and inserts records into a database. The entire operation is done within a transaction.

I find that out of about 60 messages (60 times the service being called from inside a loop) only 40 are going through to the db if I set my InstanceContextMode to PerCall. There are no errors no exceptions. The messages are just being dropped.

If I set the InstanceContextMode to Single then I see all messages getting to the db. Is the InstanceContextMode.Percall being lossy the expected behavior? Also, I do not have concurrency set. Any clarifications would be greatly helpful. Added the code. Using MySQL as the db...

EDIT My bad - I just noticed that I get an exception on the server side - {"Deadlock found when trying to get lock; try restarting transaction"}

This is because there is another transaction invoked on the same records while a transaction is under progress. Fixing it by restarting the transaction if it fails once.

The service

    [WebInvoke(UriTemplate = "employee", Method = "POST")]
    public long AddNewEmployee(EmployeeEntity newEmployee)
    {
        EmployeeRepository eRep = new EmployeeRepository();
        return eRep.AddNewEmployee(newEventEntity);                     
    }

The repository class constructor initializes the object context

    public EmployeeRepository()
    {
        bd = new EmployeeEntity();
    }

Code - The service call

    //bd is the object context 
    //there are two tables 
    internal long AddNewEmployee(EmployeeEntity newEmployee)
    {
        bool tSuccess = false;
        using (TransactionScope transaction = new TransactionScope())
        {
            try
            {
                //get existing employees
                var existingEmployees = from employee
                                        in bd.employees select employee;


                List<employee> returnedEmployees = new List<employee>();                    

                //Do some processing 
                returnedEmployees = DoSomeprocessing(existingEmployees);

                //Insert returned employees as updates
                foreach (employee e in returnedEmployees)
                {
                    bd.employees.AddObject(e);
                }

                bd.SaveChanges();
                returnedEmployees.Clear();

                //add to second table 
                bd.otherdetails.AddObject(newEmployee);
                bd.SaveChanges();


                //Transaction Complete                        
                transaction.Complete();
                tSuccess = true;

            }
            catch (Exception e)
            {
                //return something meaningful 
                return -1;                    
            }
        }

        if (tSuccess)
        {
            //End Transaction
            bd.AcceptAllChanges();
            return 200;
        }            
        else
        {
           return -1;
        }

    }

The client side just calls the service in a loop

Answer 1

I highly suggest adding global exception handling for any WCF. It has helped me save many hours of debugging and will catch any unhandled exceptions. It's a little bit more involved than global.ascx in ASP.NET

Step 1 - Implement IErroHander and IServiceBehavior

Notice inside HandleError I'm using Enterprise Library to handle the exception. You can use your custom implementation here as well.

 public class ErrorHandler : IErrorHandler, IServiceBehavior
        {        
            public bool HandleError(Exception error)
            {
                // Returning true indicates you performed your behavior.
                return true;
            }


            public void ProvideFault(Exception error, MessageVersion version, ref Message fault)
            {            
                // Log Exception

                ExceptionPolicy.HandleException(error, "ExceptionPolicy");

                // Shield the unknown exception
                FaultException faultException = new FaultException(
                    "Server error encountered. All details have been logged.");
                MessageFault messageFault = faultException.CreateMessageFault();

                fault = Message.CreateMessage(version, messageFault, faultException.Action);
            }

            private IErrorHandler errorHandler = null;

            public ErrorHandler()
            {

            }

            public ErrorHandler(IErrorHandler errorHandler)
            {
                this.errorHandler = errorHandler;
            }

            public void ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
            {
                foreach (ChannelDispatcherBase cdb in serviceHostBase.ChannelDispatchers)
                {
                    ChannelDispatcher cd = cdb as ChannelDispatcher;

                    if (cd != null)
                    {
                        cd.ErrorHandlers.Add(new ErrorHandler());
                    }
                }
            }

            public void AddBindingParameters(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase, Collection<ServiceEndpoint> endpoints, BindingParameterCollection bindingParameters)
            {
                foreach (ChannelDispatcherBase cdb in serviceHostBase.ChannelDispatchers)
                {
                    ChannelDispatcher cd = cdb as ChannelDispatcher;

                    if (cd != null)
                    {
                        cd.ErrorHandlers.Add(new ErrorHandler());
                    }
                }
            }

            public void Validate(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
            {

            }
        }

    }

Step 2 - Create Error Element

public class ErrorHandlerElement : BehaviorExtensionElement
    {
        protected override object CreateBehavior()
        {
            return new ErrorHandler();
        }

        public override Type BehaviorType
        {
            get
            {
                return typeof(ErrorHandler);
            }
        }
    }

Step 3 - Add Element to web.config

<serviceBehaviors>
        <behavior>                              
          <ErrorHandler />
        </behavior>
      </serviceBehaviors>