Github user clockfly commented on the pull request:
https://github.com/apache/storm/pull/268#issuecomment-61410622
Hi HeartSaVioR,
For acked topology, there is at least once delivery gurantee.
When a tuple is dropped, the tuple cached at spout side will timeout, and
it will report a failure to storm UI, it will be shown as "failed" count.
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