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https://issues.apache.org/jira/browse/KAFKA-1744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14201424#comment-14201424
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Jun Rao commented on KAFKA-1744:
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Evan,
I added the following explanation to the wiki.
"In general, the return messages will have offsets larger than or equal to the
starting offset. However, with compressed messages, it's possible for the
returned messages to have offsets smaller than the starting offset. The number
of such messages is typically small and the caller is responsible for filter
out those messages."
> Fetch Response contains messages prior to the requested offset
> --------------------------------------------------------------
>
> Key: KAFKA-1744
> URL: https://issues.apache.org/jira/browse/KAFKA-1744
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 0.8.1.1
> Reporter: Evan Huus
>
> As reported in https://github.com/Shopify/sarama/issues/166 there are cases
> where a FetchRequest for a particular offset returns some messages prior to
> that offset.
> The spec does not seem to indicate that this is possible; it does state that
> "As an optimization the server is allowed to return a partial message at the
> end of the message set." but otherwise implies that a request for offset X
> will only return complete messages starting at X.
> The scala consumer does seem to handle this case gracefully though, if I am
> reading it correctly (my scala is not the best):
> https://github.com/apache/kafka/blob/0.8.1/core/src/main/scala/kafka/consumer/ConsumerIterator.scala#L96-L99
> So is this a bug or just a case that needs to be added to the spec? Something
> like "As an optimization the server is allowed to return some messages in the
> message set prior to the requested offset. Clients should handle this case."?
> Although I can't imagine why sending extra data would be faster than only
> sending the necessary messages...
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