KIP-129 — Streams Exactly-Once Semantics

Accepted Kafka 1.0 StreamsTransactions

Adds exactly-once processing semantics to Kafka Streams by building on KIP-98 transactions and idempotent producer: each stream task wraps its consume-process-produce cycle in a transaction so output records and consumer offsets are committed atomically. Without this, a Streams task crash could re-process input after recovery and produce duplicate output records, violating at-least-once at the application level.

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