Github user zsxwing commented on the issue:
https://github.com/apache/spark/pull/15387
> During the original implementation I had verified that calling pause
kills the internal message buffer, which is one of the complications leading to
a cached consumer per partition.
I observed the same behavior during my debug. I found that the first
`poll(0)` will always send a request to prefetch the data. Pausing partitions
just prevents the second `poll(0)` from returning anything at here:
https://github.com/apache/kafka/blob/0.10.0.1/clients/src/main/java/org/apache/kafka/clients/consumer/internals/Fetcher.java#L527
> You dont want poll consuming messages, its not just about offset
correctness, the driver shouldnt be spending time or bandwidth doing that.
I think you have agreed that this is impossible via current KafkaConsumer
APIs as well.
However, the unknown thing to me is that if the first `poll(0)` will return
something. I saw the first `poll(0)` will always send the fetching request, but
I'm not sure that if it's possible that the response will be processed in the
first `poll(0)`. If this could happen, pausing partitions will not help in such
case since it's called after the first `poll(0)`. In addition, since it's
unclear in javadoc, it could be changed in the future. That's why I decided to
manually seek to the beginning in #15397.
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