Hello, We found a serious bug while testing flush() calls in the new producer, which is summarized in KAFKA-2042.
In general, when the producer starts up it will try to refresh metadata with empty topic list, and hence get all the topic metadata. When sending the message with some topic later, it will hence not cause the topic to be added into metadata's topic list since the metadata is available. When the data is still sitting in the accumulator and a new topic is created, that will cause metadata refresh with just this single topic, hence losing the metadata for any other topics. Under usual scenarios the messages will be sitting in the accumulator until another send() is triggered with the same topic, but with flush() as a blocking call the likelihood of this issue being exposed that messages gets blocked forever inside flush() could be largely increased. I am writing to ask if people think this problem is severe enough that requires another bug-fix release. -- Guozhang
