I'm using a WebJob to pull from my ServiceBus Queue via the trigger method and it seems to work well. The problem is I have a nightly job that pumps work into a queue, then I'd like to have another job run at the end when the queue work is finally processed to email the results. My WebJob is currently processing 16 items at a time, and I'll probably have to have multiple WebJobs running to handle the load, so I don't feel like I can just check if the Queue is empty on every trigger.
Is there a way the ServiceBus can signal when it's empty? Should I just have another recurring process running that checks every 10 minutes and fires with a daily bit value to make sure it's done? Seems inefficient. Is there some Azure pattern I'm missing here?
Azure Service Bus will not signal about empty queues. Knowing if there are any number of messages in a queue would be probably considered an anti-pattern. As Clemens Vasters said
Anytime any #Azure #ServiceBus client code looks at QueueDescription.MessageCount to determine whether to call Receive - that's a bug. Don't
Queue can contain work items at any point in time. You never know when that will end. If you have messages that represent something as a group and need to trigger an operation at the end of that group processing, you could have something that can track what work has been accomplished and when it's all done, trigger another message. It could be "I've processed X messages for session Y and therefore this work is completed, sending a notification command".
You can do this by using an instance of NamespaceManaager. It gives you the count of messages in the subscription.
NamespaceManager nsManager = NamespaceManager.CreateFromConnectionString(<connectionstring>);
var subscription = nsManager.GetSubscription(
<topicName>,<subscriptionName>);
if(subscription != null && subscription.MessageCount > 0)
//do something
If you want to avoid DLQ count then you can use subscription.MessageCountDetails.ActiveMessageCount instead in above code.
As Sean had mentioned, it would be ideal to submit a message to another queue say 'Emails' at the completion of group processing. Create a logic app with a trigger on 'when a new message is received in the 'Emails' queue and action to send out an email to the required recipients. It is pretty easy to achieve this without even a line of code.
Related
We have some issues with messages from Azure ServiceBus being read multiple times. Previously we had the same issue, which turned out to be due to lock timeout. Then, as the lock timed out the messages were read again, and their deliveryCount increased by 1 for each time the message was read. After this, we set the max delivery count to 1 to avoid resending of messages, and also increased the lock timeout to 5 minutes.
The current issue is a lot more strange.
First, messages are read at 10:45:34. Message locks are set to 10:50:34, and deliveryCount is 1. The reading says it succeeds, at 10:45:35.0. All good so far.
But then, at 10:45:35.8, the same messages are read again! And the delivery count is still 1. Both the sequence number and message id are the same in the two receive logs. This happens for a very small percentage of messages, something like 0,02% of the messages.
From what I understand, reading a message should either result in a success where the message should be removed, or an increase of deliveryCount, which in my case should send the message to DLQ. In these cases, neither happens.
I'm using ServiceBusTrigger, like this:
[FunctionName(nameof(ReceiveMessages))]
public async Task Run([ServiceBusTrigger(queueName: "%QueueName%", Connection = "ServiceBusConnectionString")]
string[] messages,
This seems to be like a bug in either the service bus or the library, any thoughts on what it could be?
That’s not the SDK but rather the specific entity. It sounds like the entity is corrupted. Delete and recreate it. If that doesn’t help, then open a support case.
On a different note, most of the time when delivery count is set to 1 is an indicator of something off. If you truly need at-most-once delivery guarantee, use ReceiveAndDelete mode instead of PeekLock.
I am experiencing a racing condition issue with my rabbitmq client. My service has multiple instances listening on a single queue, storing received messages into a db.
When they all get restarted at once, i sometimes see messages being redelivered and stored in the db twice. This is normally handled on client side by checking if the correlationid has already been stored in the db. This works 99.9% of the time (i am processing 5mill messages a day, it happens once or twice a day).
So as i said, i suspect a racing condition being responsible for this. I think i receive the message again while my first message is still being processed. So when i check i dont see it stored in the db, and in the end, store it twice.
I should not that this is a non-issue, but has been bothering me because i can't really explain what happens.
I suspect that it happens when i restart the services. I think i disconnect from the queue, while i am still processing the message, triggering rabbitmq to redeliver again to another instance that is not shutdown yet.
What i want to do is when i am stopping the service is to
tell rabbitmq that i dont want to receive further messages
wait for all currently processing messages to finish
send acks / nacks
shutdown
Right now i am first deregistering the received event
_consumerServer.Received -= MessageReceived;
then i am disposing the channel and the server
if (_channel != null)
{
_channel.Close();
_channel.Dispose();
}
if (_connectionServer != null)
{
_connectionServer.Close();
_connectionServer.Dispose();
}
The RabbitMQ team monitors this mailing list and only sometimes answers questions on StackOverflow.
Rather than try and shut down a consumer so that messages won't be redelivered, you should handle redelivery correctly. Check for and handle the case where the redelivered flag is set on a message, and act appropriately. You should also try store your messages in such a way that the store operation is idempotent - i.e. it can happen multiple times and you will only have one record in your database.
Please see the guidelines that the team have provided here:
https://www.rabbitmq.com/reliability.html#consumer
We're using ActiveMQ locally to transfer data between 5 processes that turn simultaneously.
I have some data I need to send to a process, both at runtime (which works perfectly fine), but also a default value on start. Thing is it is published when the process starts, it just doesn't read because it wasn't subscribed to the topic at the time the data was sent.
I have multiple solutions : I could delay the first publishing for a moment so that the process has time to launch (which doesn't seem very appealing) ; or is there a way to send all stored previously non-treated messages to some process that just subscribed ?
I'm coding in C#.
I don't have any experience with ActiveMQ, but other message system usually have an option which marks the subscription as persistent, which means that; after the first subscription; the message queue itself checks if a certain message is delivered to that system and retries with a timeout. In this scenario you need to start the receiver at least 1 time.
If this is not an option and you want to plug in receiver afterwards, you might want to consider a setup of your messages which allows you to retrieve the full state, i.e. if you send total-messages instead of differential- messages.
After a little google, I came upon this definition durable subscribers, I hope this helps:
See:
http://activemq.apache.org/how-do-durable-queues-and-topics-work.html
and
http://activemq.apache.org/manage-durable-subscribers.html
since you are using C# client i don't konw if this is supported
topic = new ActiveMQTopic("TEST.Topic?consumer.retroactive=true");
http://activemq.apache.org/retroactive-consumer.html
So, another solution is to configure this behavior on the broker side by adding that to the activemq.xml and restart :
The subscription recovery policy allows you to go back in time when
you subscribe to a topic.
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic=">" >
<subscriptionRecoveryPolicy>
<timedSubscriptionRecoveryPolicy recoverDuration="10000" />
<fixedCountSubscriptionRecoveryPolicy maximumSize="10000" />
</subscriptionRecoveryPolicy>
</policyEntry>
</policyEntries>
</policyMap>
</destinationPolicy>
http://activemq.apache.org/subscription-recovery-policy.html
I went around the issue by sending a message from each process when they're launched back to the main one, and then only sending the info I needed to send.
We have pub/sub application that involves an external client subscribing to a Web Role publisher via an Azure Service Bus Topic. Our current billing cycle indicates we've sent/received >25K messages, while our dashboard indicates we've sent <100. We're investigating our implementation and checking our assumptions in order to understand the disparity.
As part of our investigation we've gathered wireshark captures of client<=>service bus traffic on the client machine. We've noticed a regular pattern of communication that we haven't seen documented and would like to better understand. The following exchange occurs once every 50s when there is otherwise no activity on the bus:
The client pushes ~200B to the service bus.
10s later, the service bus pushes ~800B to the client. The client registers the receipt of an empty message (determined via breakpoint.)
The client immediately responds by pushing ~1000B to the service bus.
Some relevant information:
This occurs when our web role is not actively pushing data to the service bus.
Upon receiving a legit message from the Web Role, the pattern described above will not occur again until a full 50s has passed.
Both client and server connect to sb://namespace.servicebus.windows.net via TCP.
Our application messages are <64 KB
Questions
What is responsible for the regular, 3-packet message exchange we're seeing? Is it some sort of keep-alive?
Do each of the 3 packets count as a separately billable message?
Is this behavior configurable or otherwise documented?
EDIT:
This is the code the receives the messages:
private void Listen()
{
_subscriptionClient.ReceiveAsync().ContinueWith(MessageReceived);
}
private void MessageReceived(Task<BrokeredMessage> task)
{
if (task.Status != TaskStatus.Faulted && task.Result != null)
{
task.Result.CompleteAsync();
// Do some things...
}
Listen();
}
I think what you are seeing is the Receive call in the background. Behind the scenes the Receive calls are all using long polling. Which means they call out to the Service Bus endpoint and ask for a message. The Service Bus service gets that request and if it has a message it will return it immediately. If it doesn't have a message it will hold the connection open for a time period in case a message arrives. If a message arrives within that time frame it will be returned to the client. If a message is not available by the end of the time frame a response is sent to the client indicating that no message was there (aka, your null BrokeredMessage). If you call Receive with no overloads (like you've done here) it will immediately make another request. This loop continues to happend until a message is received.
Thus, what you are seeing are the number of times the client requests a message but there isn't one there. The long polling makes it nicer than what the Windows Azure Storage Queues have because they will just immediately return a null result if there is no message. For both technologies it is common to implement an exponential back off for requests. There are lots of examples out there of how to do this. This cuts back on how often you need to go check the queue and can reduce your transaction count.
To answer your questions:
Yes, this is normal expected behaviour.
No, this is only one transaction. For Service Bus you get charged a transaction each time you put a message on a queue and each time a message is requested (which can be a little opaque given that Recieve makes calls multiple times in the background). Note that the docs point out that you get charged for each idle transaction (meaning a null result from a Receive call).
Again, you can implement a back off methodology so that you aren't hitting the queue so often. Another suggestion I've recently heard was if you have a queue that isn't seeing a lot of traffic you could also check the queue depth to see if it was > 0 before entering the loop for processing and if you get no messages back from a receive call you could go back to watching the queue depth. I've not tried that and it is possible that you could get throttled if you did the queue depth check too often I'd think.
If these are your production numbers then your subscription isn't really processing a lot of messages. It would likely be a really good idea to have a back off policy to a time that is acceptable to wait before it is processed. Like, if it is okay that a message sits for more than 10 minutes then create a back off approach that will eventually just be checking for a message every 10 minutes, then when it gets one process it and immediately check again.
Oh, there is a Receive overload that takes a timeout, but I'm not 100% that is a server timeout or a local timeout. If it is local then it could still be making the calls every X seconds to the service. I think this is based on the OperationTimeout value set on the Messaging Factory Settings when creating the SubscriptionClient. You'd have to test that.
I have an NServiceBus application for which a given message may not be processed due to some external event not having taken place. Because this other event is not an NSB event I can't implement sagas properly.
However, rather than just re-queuing the message (which would cause a loop until that external event has occurred), I'm wrapping the message in another message (DelayMessage) and queuing that instead. The DelayMessage is picked up by a different service and placed in a database until the retry interval expires. At which point, the delay service re-queues the message on the original queue so another attempt can be made.
However, this can happen more than once if that external event still hasn't taken place, and in the case where that even never happens, I want to limit the number of round trips the message takes. This means the DelayMessage has a MaxRetries property, but that is lost when the delay service queues the original message for the retry.
What other options am I missing? I'm happy to accept that there's a totally different solution to this problem.
Consider implementing a saga which stores that first message, holding on to it until the second message arrives. You might also want the saga to open a timeout as well so that your process won't wait indefinitely if that second message got lost or something.