Scaling an Azure Event Hub: Throughput units

When navigating to the scale tab of an event hub there are only two options you can choose: messaging tier and eventhub throughput units.

Scale settings

The messaging tier enables features and sets the amount you pay for messages or connections. You can find more info on the Azure website.

A throughput unit (TU) has quite a direct impact on the performance. A TU currently has these limits: 1 MB/s Ingress, 2 MB/s egress, and up to 84 GB of event storage. The default value is 1 TU.

In the picture below you can see that I had one cloud service pushing messages to an event hub until 10:00. I then scaled out the service to 20 instances. This resulted in about twice the amount of messages being sent (from 200k to 400k), not really what you expect. I was also getting more errors, from time to time the event hub was sending back server busy messages.


At about 10:30 I increased the TU from 1 to 3, this not only stopped the errors from occurring but further increased the throughput from 400k to over 1 million messages being received on the event hub per 5 minutes.