delivery semantics ของ Kafka มีอะไรบ้าง (at-least-once, exactly-once)?

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