Adding such callback functionality is proposed for Kafka 0.9, see [Proposed Producer API](https://cwiki.apache.org/confluence/display/KAFKA/Client+Rewrite#ClientRewrite-ProposedProducerAPI).
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If the consumer never crashed it could just store this position in memory, but if the producer fails and we want this topic partition to be taken over by another process the new process will need to choose an appropriate position from which to start processing.
I think that "producer" should be replaced by "consumer".
I do not propose a patch because I am unsure where the sources are. Is that the HTML files in the SVN repository? Or is there some git repository somewhere?