NServiceBus Pub/Subscribe using SQLServer transport - can the subscriber scale out?

Question

Using the latest version of NServiceBus 4.4 I believe.

We are looking to implement NServiceBus and this section is using SQLServer as a transport. We want to pub/subscribe, which is fine but how would it work with scaling out the subscribers?

I have done a PoC where I ran the recieving endpoint of a SQLServer transport multiple times and when a message came in, the first instance of the running reciever got the message and processed it, resulting in the other process NOT processing it, which is correct.

In a pub/subscribe architecture using SQLServer, would this same method of running multiple instances of the subscriber work and since we are using a common queue (SQLServer) it will just sort itself out and not process the message multiple times?

Answer 1

When using SQL Server persistence, the subscribers for your events and messages are held in the Subscription table within the NServiceBus database, so you can check which endpoints are subscribing to what messages or events by viewing the contents of that.

It's worth noting that you can only publish "message" classes with NServiceBus that are implementing the IEvent interface (unless you make use of unobtrusive mode).

When you publish a message or event using bus.Publish, all subscribers to that type will subscribe to it, as long as the individual endpoint names are different.

More information from Particular Software is here:

And here.