Does Azure client .OnMessage generate billable request for empty queues?

Question

You can subscribe to asynchronous updates from Azure topics and queues by using SubscriptionClient/QueueClient's .OnMessage call which will presumably create a separate thread polling the topic/queue with default settings and calling a defined callback if it receives anything.

Azure website says that receiving a message is a billable action, which is understandable. However, it isn't clear enough if each those poll requests are considered billable even when they do not return anything, i.e. the queue in question has no pending messages.

Answer 1

Based on the Azure Service Bus Pricing FAQ - the answer to your question is yes

In general, management operations and “control messages,” such as completes and deferrals, are not counted as billable messages. There are two exceptions:

Null messages delivered by the Service Bus in response to requests against an empty queue, subscription, or message buffer, are also billable. Thus, applications that poll against Service Bus entities will effectively be charged one message per poll.

Setting and getting state on a MessageSession will also result in billable messages, using the same message size-based calculation described above.

Given the price is $0.01 per 10,000 messages, I don't think you should worry too much about that.