Question

I have developed a Monitoring application. So there i have used a Timer function in order to check some values in a SQL Table.

though there are so many function it gives an following error for one function called getLogEntry()

message>Transaction (Process ID 84) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.</message>
<innerMessage>
</innerMessage>
<source>.Net SqlClient Data Provider</source>
<stackTrace>at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   at System.Data.SqlClient.SqlDataReader.HasMoreRows()
   at System.Data.SqlClient.SqlDataReader.ReadInternal(Boolean setTimeout)
   at ShiftAlertSystem.DBAccess.getLogEntry(Int32 nEventLogIdn, connections cn)</stackTrace>
    <createdAt>2012/06/18 13:10:47</createdAt>

This is the implementation of the function

public LogEntry getLogEntry(int nEventLogIdn, connections cn)
    {
        lock (_objLock)
        {
            LogEntry lgEntObj = new LogEntry();
             SqlConnection NewCon3 = new SqlConnection();
             SqlCommand newCmd2 = null;
             SqlDataReader dr = null;

             try
             {


                 string connectString;
                 // Configuration config = ConfigurationManager.u
                 string DataSource = cryptIT.Decrypt(cn.DataSource_bio);
                 string initialCatalog = cryptIT.Decrypt(cn.InitialCatalog_bio);
                 string user = cryptIT.Decrypt(cn.user_bio);
                 string password = cryptIT.Decrypt(cn.password_bio);
                 bool intergratedSecurity = cn.IntegratedSecurity_bio;

                 if (intergratedSecurity)
                 {
                     connectString = "Data Source=" + DataSource + ";Initial Catalog=" + initialCatalog + ";Integrated Security=True";
                 }
                 else
                 {
                     connectString = "Data Source=" + DataSource + ";Initial Catalog=" + initialCatalog + ";User ID=" + user + ";Password=" + password;
                 }

                 NewCon3 = new SqlConnection(connectString);
                 NewCon3.Open();



                 newCmd2 = NewCon3.CreateCommand();
                 newCmd2.Connection = NewCon3;
                 newCmd2.CommandType = CommandType.Text;
                 newCmd2.CommandText = @"
                                 SELECT [nUserID]
                                        ,[sUserName]
                                        ,dateadd(s,[nDateTime],'1970/1/1') AS LogDateTime
                                        ,[nEventIdn]
                                        ,[nTNAEvent]
                                        ,[TB_READER].[nReaderIdn]
                                        ,[sName]
                                 FROM 
                                        [TB_EVENT_LOG]
                                        ,[TB_USER]
                                        ,[TB_READER]
                                WHERE 

                                        [nEventLogIdn] = " + nEventLogIdn +
                                         @" AND
                                        [TB_EVENT_LOG].[nUserID] = [TB_USER].[sUserID]
                                        AND
                                        [nFlag]= 1
                                        AND
                                        [TB_EVENT_LOG].[nReaderIdn]=[TB_READER].[nReaderIdn]"
                                         ;
                 dr = newCmd2.ExecuteReader();

                 if (dr != null && dr.Read())
                 {
                     lgEntObj.nUserID = dr.GetInt32(0);
                     lgEntObj.nUserName = dr.GetString(1);
                     lgEntObj.LogDateTime = dr.GetDateTime(2);
                     lgEntObj.nEventIdn = dr.GetInt32(3);
                     lgEntObj.nTNAEvent = dr.GetInt16(4);
                     lgEntObj.nReaderIdn = dr.GetInt32(5);
                     lgEntObj.sName = dr.GetString(6);
                 }
                 dr.Close();
                 newCmd2.Dispose();
                 // NewCon.Close();
                 NewCon3.Close();

                 return lgEntObj;
             }
             catch (Exception exc)
             {
                 CenUtility.ErrorLog.CreateLog(exc);
                 return null;
             }

             finally
             {
                 if (dr != null)
                     dr.Close(); 

                 if(newCmd2 != null)
                     newCmd2.Dispose();


                     NewCon3.Close();


             }


        }
    }

Thanks in advance

Answer 1

You may want to refer to this question for some more helpful suggestions.

I use the following pattern for database retries; in this instance, we return a DataTable but the pattern is the same regardless; you detect a SqlDeadlock or Timeout based on the SqlException Number, and retry, up to a maximum number of n times.

    public DataTable DoSomeSql(int retryCount = 1)
    {
        try
        {
            //Run Stored Proc/Adhoc SQL here

        }
        catch (SqlException sqlEx)
        {
            if (retryCount == MAX_RETRY_COUNT) //5, 7, Whatever
            {
                log.Error("Unable to DoSomeSql, reached maximum number of retries.");
                throw;
            }

            switch (sqlEx.Number)
            {
                case DBConstants.SQL_DEADLOCK_ERROR_CODE: //1205
                    log.Warn("DoSomeSql was deadlocked, will try again.");
                    break;
                case DBConstants.SQL_TIMEOUT_ERROR_CODE: //-2
                    log.Warn("DoSomeSql was timedout, will try again.");
                    break;
                default:
                    log.WarnFormat(buf.ToString(), sqlEx);
                    break;
            }

            System.Threading.Thread.Sleep(1000); //Can also use Math.Rand for a random interval of time
            return DoSomeSql(asOfDate, ++retryCount);
        }
    }