Kafka支持不同的交付保证 — at-most-once、at-least-once和exactly-once — 这些保证决定了消息是否可能丢失或重复。理解这些保证以及如何实现它们对于构建可靠的系统很重要。
三种交付语义
AT-MOST-ONCE → messages may be LOST but never duplicated:
→ commit offset BEFORE processing → if processing fails, the message is skipped (lost)
→ for: when occasional loss is acceptable and duplicates are not (rare)
AT-LEAST-ONCE → messages are never lost but may be DUPLICATED:
→ commit offset AFTER processing → if a crash occurs before commit, the message is
reprocessed (duplicate) → requires IDEMPOTENT processing
→ the common default; safe (no loss) but handle duplicates
EXACTLY-ONCE → each message is processed exactly once (no loss, no duplicates):
→ the strongest, but hardest; requires Kafka transactions + idempotent producers
