State & Time — Week 2 CheckWeek 2 of Stream Processing: the hard parts — event time vs processing time, watermarks, and state that survives failure.

Event time vs processing time: which failure does EVENT-time processing prevent?

A watermark of T asserts what, exactly?

Late data arrives after its window closed. The three honest options are:

Why does streaming state need CHECKPOINTS rather than just replaying the input on failure?

One key in your keyed state receives 100× the traffic of others (a celebrity account, a default value). The classic symptom and fix:

An idle partition (no events for hours) can stall the entire job's output. Why?