Multiple Simultaneous SQL Connection Timeouts In Multithreaded Windows Service

Question

I have a multithreaded Windows Service I\'ve developed with VS 2010 (.NET 4.0) which can have anywhere from a few to a few dozen threads, each retrieving data from a slow se

Answer 1

I have been able to somewhat reliably reproduce this problem. I have a service that when a processing job is requested it kicks off processing in a new appdomain / thread. This thread will execute 10 to 16 database queries simultaneously. When I run 30 of these jobs one after another then a random one or two of the jobs will crash with the timeout error.

I changed the connection string to turn off Connection Pooling with Pooling=false and then the error changed to the following. This gets thrown 3 or 4 times inside an aggregate exception, since the connections are happening inside a Parallel.For

System.Data.SqlClient.SqlException: Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning()
   at System.Data.SqlClient.TdsParserStateObject.ReadSniError(TdsParserStateObject stateObj, UInt32 error)
   at System.Data.SqlClient.TdsParserStateObject.ReadSni(DbAsyncResult asyncResult, TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParserStateObject.ReadNetworkPacket()
   at System.Data.SqlClient.TdsParser.ConsumePreLoginHandshake(Boolean encrypt, Boolean trustServerCert, Boolean& marsCapable)
   at System.Data.SqlClient.TdsParser.Connect(ServerInfo serverInfo, SqlInternalConnectionTds connHandler, Boolean ignoreSniOpenTimeout, Int64 timerExpire, Boolean encrypt, Boolean trustServerCert, Boolean integratedSecurity)
   at System.Data.SqlClient.SqlInternalConnectionTds.AttemptOneLogin(ServerInfo serverInfo, String newPassword, Boolean ignoreSniOpenTimeout, TimeoutTimer timeout, SqlConnection owningObject)
   at System.Data.SqlClient.SqlInternalConnectionTds.LoginWithFailover(Boolean useFailoverHost, ServerInfo primaryServerInfo, String failoverHost, String newPassword, Boolean redirectedUserInstance, SqlConnection owningObject, SqlConnectionString connectionOptions, TimeoutTimer timeout)
   at System.Data.SqlClient.SqlInternalConnectionTds.OpenLoginEnlist(SqlConnection owningObject, TimeoutTimer timeout, SqlConnectionString connectionOptions, String newPassword, Boolean redirectedUserInstance)
   at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, Object providerInfo, String newPassword, SqlConnection owningObject, Boolean redirectedUserInstance)
   at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection)
   at System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup)
   at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
   at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
   at System.Data.SqlClient.SqlConnection.Open()
   at Tps.PowerTools.CoreEngine.V5.DataAccess.DataContext.ExecuteQuery(PtQuery query, ValueStore`1 store, String readerDescription) in C:\SourceCode\Tps.PowerToolsV1\Trunk\Libraries\CoreEngine\CoreEngine.V5\DataAccess\DataContext.cs:line 326
   at Tps.PowerTools.CoreEngine.V5.DataAccess.DataContext.b__15(PtQuery query) in C:\SourceCode\Tps.PowerToolsV1\Trunk\Libraries\CoreEngine\CoreEngine.V5\DataAccess\DataContext.cs:line 302
   at System.Threading.Tasks.Parallel.<>c__DisplayClass32`2.b__30()
   at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask)
   at System.Threading.Tasks.Task.<>c__DisplayClass7.b__6(Object )