The 2 main types of stream processing done are:
1. Stateless: Where every event is handled completely independent from the preceding events.
2. Stateful: Where a “state” is shared between events and therefore past events can influence the way current events are processed.
Stateless stream processing is easy to scale up because events are processed independently. But Stateful stream processing is difficult to scale up because the “state” needs to be shared across the events.
Himanshu does point out alternatives, but this isn’t a comparison exercise.