Google PubSub is a great product. The primary benefit of K2 is cost, particularly for longer retention periods. Being backed by object storage means that we can store data extremely cheaply compared to disk backed solution, and we pass that on in our pricing.

Compared to self-hosted or cloud-hosted Kafka (e.g., Amazon MSK or Confluent), K2 is much cheaper, and fully serverless. There are no clusters to manage or scale, and consistent performance even as you vastly increase the amount of data.

The main downside is produce (and end to end) latency is higher (around 1s p99) than systems that rely on local disk replication, like Kafka.

So it's great if you're trying to move a huge amount of data around, or for use cases where cost is more important than latency.

Having built a hobo version of something similar (serving a minimal subset of the Kafka API on top of CosmoDB): there’s also the hybrid scenario where the cheap serverless streams are used for scalability and broadcast while a low-latency core is maintained on sharply reduced compute resources. An 80/20 approach that saves a lot and, in our case, reduced cluster (mis)management risks at the same time.

In our case BLOB and large document transfers were handled in parallel, merging them together through object storage is a highly appealing package. Great work!