Episode idea: cursor management

[caibirdme]

Describe a topic you want to learn (required)

How pulsar handles cursor management especially for the cursor in shared subscription mode.

Why do you want to learn this topic? (required)

In shared mode, msg is consumed concurrently, and there's no order guranteed. Does pulsar need to store the ack info for every message in the topic? How does it achieve that and how to know which one should be redelivered next time

Reference (optional)

cursor in pulsar, too simple and doesn't cover the shared mode.