Question about Event Hub

hi,

   Background: The purpose for the app is to find out ServiceBus event hub's max capacity for reading/writing messages.

   environment: 2 senders which sending batch of data per 10 seconds to the event hub, while 2 receivers are receiving messages from the event hub, then either insert into table storage/ blob storage. (also the reading/writing capacity to storage will be found out.)

   each sender: current environment settings: total devices =500, total tags=50000, sample rate=10 seconds

it means 500 commit per 10 seconds, each commit contains 100 columns which is 17482 bytes in total.

however, after almost 3 mins, the log shows below ServerBusyException.

My question is what the root cause for the throttled.

Here is the log

[2016-05-04 02:41:55,751]  1 -- INFO  -- LogInfo [WriteLog] -- step 2: Launch agent instances to submit data.........

 ...............................

[2016-05-04 02:44:11,151]  3 -- ERROR -- LogError [WriteLog] -- Submit data failed.
Microsoft.ServiceBus.Messaging.ServerBusyException: The request was terminated because the entity is being throttled. Error code : 50002. Please wait 4 seconds and try again. TrackingId:a30dd90a000066430007ba7457296147_G18_B5, Reference:b315d19a-405a-49d9-b118-f72e820b8e2e, Timestamp:5/4/2016 2:44:09 AM
   at Microsoft.ServiceBus.Common.AsyncResult.End[TAsyncResult](IAsyncResult result)
   at Microsoft.ServiceBus.Messaging.MessageSender.EndSendEventData(IAsyncResult result)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean requiresSynchronization)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()

Here is the C# code

EventHubClient client = EventHubClient.CreateFromConnectionString(
                                ServiceBusSettings.ServiceBusConnectionString,
                                ServiceBusSettings.DefaultTagvalueEventHubName);
            string dataStr = string.Empty;
                try
                {
                    client.RetryPolicy = RetryPolicy.Default;
                    dataStr = JsonConvert.SerializeObject(data);
                    //LogHelper.WriteLog(string.Format("each message = {0} bytes", dataStr.Length));
                    var dataInByte = Encoding.UTF8.GetBytes(dataStr);

                         var eventData = new EventData(dataInByte) { PartitionKey = data.CollectionGroupKey };
                        await client.SendAsync(eventData);
                        await client.CloseAsync();
                        tagsCount.AddCount(data.Samples.Sum(s => s.TagValues.Count()));
                        LogHelper.WriteLog(string.Format("Submitted total {0} tags.", tagsCount.TagsCount));
                }
                catch (Exception ex)
                {
                    if (!client.IsClosed)
                    {
                        client.Abort();
                    }

                    LogHelper.WriteLog(string.Format("Submit data failed. current data size ={0} bytes.", dataStr.Length), ex);
                }