We are running NServiceBus 4.6.5 in a distributor/worker configuration and are preparing for our peak sales period where the system will be under much heavier load than normal.
One thing we have found during our performance tests is that the distributor tends to go into high CPU usage if a backlog of messages appears on the distributor’s input queue. We have seen it go as high as 90% if there are as few as 1,000 messages on the input. The distributor is running on a reasonably spec’d machine: it’s a 2-node Windows 2012 cluster, with each node a 2 x dual-core 2.3HGz CPU and 8GB of RAM.
Is this normal? What is the process doing that requires such high CPU usage?