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POSQLException on ADO.Net SqlCommand.EndExecuteReader
 

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    <p>I'm trying to call out to a stored procedure asynchronously with multiple calls on the one connection via ADO.Net <code>SqlCommand</code>.</p> <p>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:</p> <blockquote> <p>System.Data.SqlClient.SqlException (0x80131904): A severe error occurred on the current command. The results, if any, should be discarded.<br> at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolea n breakConnection)<br> at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception , Boolean breakConnection)<br> at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()<br> at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cm dHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, Tds ParserStateObject stateObj)<br> at System.Data.SqlClient.SqlDataReader.ConsumeMetaData()<br> at System.Data.SqlClient.SqlDataReader.get_MetaData()<br> at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, Run Behavior runBehavior, String resetOptionsString)<br> at System.Data.SqlClient.SqlCommand.CompleteAsyncExecuteReader()<br> at System.Data.SqlClient.SqlCommand.InternalEndExecuteReader(IAsyncResult asy ncResult, String endMethod)<br> at System.Data.SqlClient.SqlCommand.EndExecuteReader(IAsyncResult asyncResult )</p> </blockquote> <p>The SQL logs is showing the following error repeatedly:</p> <blockquote> <p>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.</p> </blockquote> <p>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.</p> <p>I created the following console app which is exhibiting the same behaviour on my machine, the <code>DummySp</code> I created just returns as soon as its called</p> <pre><code>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&lt;BusinessObject&gt; BusinessObjects = new List&lt;BusinessObject&gt; { 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&lt;SqlCommand, BusinessObject&gt;(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&lt;SqlCommand, BusinessObject&gt;)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(); } } } } </code></pre> <p>Any ideas on how to overcome this?</p> <p>Thanks</p>
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    1. USmarc_s
    1. USgouldos
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    1. COThanks for preparing your question so well.
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      1. USSzymon
    2. COThis works for me fine both on SQL Server 2008 Express and full SQL Server 2008 R2.
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      1. USSzymon
    3. COThanks 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.
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      1. USgouldos
 

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