Azure Service Bus - Determine Number of Active Connections (Topic/Queue)

Question

Since Azure Service Bus limits the maximum number of concurrent connections to a Queue or Topic to 100, is there a method that we can use to query our Queues/Topics to determine how many concurrent connections there are?

We are aware that we can capture the throttling events, but would very much prefer an active approach, where we can proactively increase or decrease the number of Queues/Topics when the system is under a heavy load.

The use case here is a process waiting for a reply message, where the reply is coming from a long-running process, and the subscription is using a Correlation Filter to facilitate two-way communication between the Publisher and Subscriber. Thus, we must have a BeginReceive() going in order to await the response, and each such Publisher will be consuming a connection for the duration of their wait time. The system already balances load across multiple Topics, but we need a way to be proactive about how many Topics are created, so that we do not get throttled too often, but at the same time not have an excess of Topics for this purpose.

Answer 1

I don't believe it is currently possile to query the listener counts. I think that the subscriber object also figures into that so in theory, if you have up to 2000 subscribers per topic and if each allows up to 100 connections, that's alot of potential connections. We just need to keep in mind that subscribers are cooperative (each gets a copy of all messages) and receivers on subscriers are competitive (only one gets it).

I've also seen unconfirmed reports of performance delays when you start running > 1,000 subscribers so make sure you test this scenario.

But... given your scenario, I'd deduce that performance time likely isn't the biggest factor (you have long running processes already). So introducing a couple seconds lag into the workflow likely won't be critical. If that's the case, I'd set the timeout for your BeginRecieve to something fairly short (couple seconds) and have a sleep/wait delay between attempts. This gives other listeners an opportnity to get messsages as well. We might also want to consider an approach where we attempt to recieve multiple messages and then assign them out other processes for processing (coorelation in this case?).

Juts some thoughts.