Exactly-Once, State & Replay — Senior ScreeningA senior-loop round: reason about watermark mechanics, state cost, exactly-once boundaries and replay semantics.

An operator reads six Kafka partitions; one partition stops receiving data. What happens to the operator's watermark?

A stalled watermark is dangerous beyond missing output because…

A one-hour sliding window with a one-minute slide keeps how many copies of each event in state, roughly?

Exactly-once 'end to end' additionally requires the sink to…

A bug is fixed and the job is replayed from Monday's offsets against a billing sink that charges cards. What is the correct precaution?

Rescaling a keyed job from 8 to 16 parallel tasks requires…

RocksDB state backend versus heap state: which statement is right?

Unaligned checkpoints help when…

An upsert (changelog) stream differs from an append stream in that…

Retiring a Lambda architecture for a single streaming path is justified when…