This is a sister post to one I am writing about multi-topic subscriptions with Apache Kafka that you can read soon on the Cloud Karafka blog (link coming soon). I will provide a summary of those results before we get started with Apache Pulsar. The run the same tests in my tests of both technologies.
The objective is to get an understanding of what to expect from multi-topic subscriptions, specifically we are testing message ordering. Message ordering is a fundamental component of messaging systems and even though cross topic ordering is not guaranteed by Pulsar or Kafka, I find it interesting and useful to know what to expect.