SQLException on ADO.Net SqlCommand.EndExecuteReader

Question

I'm trying to call out to a stored procedure asynchronously with multiple calls on the one connection via ADO.Net SqlCommand.

The calls are being triggered on a timer every half a second and for some of the time I am receiving the results back as expected and sometimes I am receiving the following error:

System.Data.SqlClient.SqlException (0x80131904): A severe error occurred on the current command. The results, if any, should be discarded.
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolea n breakConnection)
at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception , Boolean breakConnection)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()
at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cm dHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, Tds ParserStateObject stateObj)
at System.Data.SqlClient.SqlDataReader.ConsumeMetaData()
at System.Data.SqlClient.SqlDataReader.get_MetaData()
at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, Run Behavior runBehavior, String resetOptionsString)
at System.Data.SqlClient.SqlCommand.CompleteAsyncExecuteReader()
at System.Data.SqlClient.SqlCommand.InternalEndExecuteReader(IAsyncResult asy ncResult, String endMethod)
at System.Data.SqlClient.SqlCommand.EndExecuteReader(IAsyncResult asyncResult )

The SQL logs is showing the following error repeatedly:

The server will drop the connection, because the client driver has sent multiple requests while the session is in single-user mode. This error occurs when a client sends a request to reset the connection while there are batches still running in the session, or when the client sends a request while the session is resetting a connection. Please contact the client driver vendor.

My connection string has MARS and Async=true set. I'm currently using SQL Server 2008 Express although the target client will be a fully fledged SQL Server instance.

I created the following console app which is exhibiting the same behaviour on my machine, the DummySp I created just returns as soon as its called

public class BusinessObject
{
    public string  Name {get; set;}
    public void UpdateData(DataTable dataTable)
    {
        Console.WriteLine("{0}: new data received.",Name);
    }
}

public class Program
{
    private const string SpName = "DummySp";
    private const string ConnectionsString = @"Data Source=(local)\sqlexpress;Initial Catalog=Test;Integrated Security=SSPI;Connection Timeout=3600";

    private static readonly object DbRequestLock = new object();
    private static readonly ManualResetEvent DatabaseRequestsComplete = new ManualResetEvent(false);
    private static int _databaseRequestsLeft;
    private static Timer _timer;

    static readonly List<BusinessObject> BusinessObjects = new List<BusinessObject>
    {
        new BusinessObject{Name = "A"},
        new BusinessObject{Name = "B"},
        new BusinessObject{Name = "C"},
    };

    static void Main(string[] args)
    {
        _timer = new Timer(DoQuery, null, 0, 500);

        Console.ReadLine();

        _timer.Dispose();         
    }

    private static void DoQuery(object state)
    {
        try
        {
           lock (DbRequestLock)
            {

                DatabaseRequestsComplete.Reset();
                _databaseRequestsLeft = BusinessObjects.Count;

                var builder = new SqlConnectionStringBuilder(ConnectionsString)
                    {
                        AsynchronousProcessing = true,
                        MultipleActiveResultSets = true
                    };

                using (var connection = new SqlConnection(builder.ConnectionString))
                {
                    connection.Open();

                    foreach (var businessObject in BusinessObjects)
                    {
                        var command = new SqlCommand(SpName, connection) { CommandType = CommandType.StoredProcedure };

                        command.BeginExecuteReader(Callback, new Tuple<SqlCommand, BusinessObject>(command, businessObject));
                    }

                    // need to wait for all to complete before closing the connection
                    DatabaseRequestsComplete.WaitOne(10000);
                    connection.Close();
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Following error occurred while attempting to update objects: " + ex);
        }
    }

    private static void Callback(IAsyncResult result)
    {
        try
        {
            var tuple = (Tuple<SqlCommand, BusinessObject>)result.AsyncState;
            var businessObject = tuple.Item2;

            using (SqlCommand command = tuple.Item1)
            {
                using (SqlDataReader reader = command.EndExecuteReader(result))
                {
                    using (var table = new DataTable(businessObject.Name))
                    {
                        table.Load(reader);

                        businessObject.UpdateData(table);
                    }
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
        }
        finally
        {
            // decrement the number of database requests remaining and, if there are 0 fire the mre
            if (Interlocked.Decrement(ref _databaseRequestsLeft) == 0)
            {
                DatabaseRequestsComplete.Set();
            }
        }
    }
}

Any ideas on how to overcome this?

Thanks

This works for me fine both on SQL Server 2008 Express and full SQL Server 2008 R2. — Szymon
Thanks for trying. What number of cores does your machine have? I've tried it on 3 different machines, 2 with 4 cores and 1 which has 2 hyperthreaded cores, all exhibit the same behaviour. If the DB server is on a seperate machine the issue is not quite so apparent. Putting in a delay to the SP increases the occurances making me suspect that there is an issue with the same SP being called on the same connection. If I use seperate connections for each command I the problem dissapears. — gouldos

gouldos gouldos · Accepted Answer · 2013-10-30T09:11:20

This isn't answering my question directly and so I haven't marked it as such but I thought it was worth showing the alternative of having a single connection per object as this seems to circumvent the issue...

 private static void DoQuery(object state)
    {
        try
        {
            lock (DbRequestLock)
            {

                var builder = new SqlConnectionStringBuilder(ConnectionsString)
                    {
                        AsynchronousProcessing = true,
                    };

                DatabaseRequestsComplete.Reset();
                _databaseRequestsLeft = BusinessObjects.Count;

                foreach (var businessObject in BusinessObjects)
                {
                    var newConnection = new SqlConnection(builder.ConnectionString);
                    newConnection.Open();

                    var command = new SqlCommand(SpName, newConnection) { CommandType = CommandType.StoredProcedure };

                    command.BeginExecuteReader(Callback, new Tuple<SqlCommand, BusinessObject>(command, businessObject),CommandBehavior.CloseConnection);

                }
                // need to wait for all to complete                    DatabaseRequestsComplete.WaitOne(10000);
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Following error occurred while attempting to update objects: " + ex);
        }
    }

    private static void Callback(IAsyncResult result)
    {
        var tuple = (Tuple<SqlCommand, BusinessObject>)result.AsyncState;
        var businessObject = tuple.Item2;
        SqlCommand command = tuple.Item1;
        try
        {
            using (SqlDataReader reader = command.EndExecuteReader(result))
            {
                using (var table = new DataTable(businessObject.Name))
                {
                    table.Load(reader);

                    businessObject.UpdateData(table);
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
        }
        finally
        {
            // decrement the number of database requests remaining and, if there are 0 fire the mre
            if (Interlocked.Decrement(ref _databaseRequestsLeft) == 0)
            {
                DatabaseRequestsComplete.Set();
            }

            try
            {
                command.Dispose();
                command.Connection.Dispose();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
        }
    }

SQLException on ADO.Net SqlCommand.EndExecuteReader

1 Answers