kafka streams guarantee Extract once?

[? ? <fu...@live.com>]

Hi:
I used kafka streams for days.
and I use it for data real-time analysis.
that is my flow
A (source topic)----------> B (internal topic) ----------> C(sink-topic)
and there ara two process program here.
1).consumed A topic to downstream B topic
2).consumed B topic to downstream C topic
but  in one of that condition.there are also due to consumer commit offset or producer retries or session time out
the downstream topic message logsize is larger than upstream Topic
how  to avoid this ?
https://www.confluent.io/blog/enabling-exactly-kafka-streams/
I miss understand with this blog
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