Hi devs, I'm trying to replace deprecated poll(long) with poll(Duration), and realized there's no alternative which behaves exactly same as poll(0), as poll(0) has been used as a hack to only update metadata instead of pulling records. poll(Duration.ZERO) wouldn't behave same since even updating metadata will be timed-out. So now end users would need to give more timeout and even pull some records even they're only interested in metadata.
I looked back some KIPs which brought the change, and "discarded" KIP (KIP-288 [1]) actually proposed a new API which only pulls metadata. KIP-266 [2] is picked up instead but it didn't cover all the things what KIP-288 proposed. I'm seeing some doc explaining poll(0) hasn't been supported officially, but the hack has been widely used and they can't be ignored. Kafka test code itself relies on either deprecated poll(0), or updateAssignmentMetadataIfNeeded, which seems to be private API only for testing. (Btw, I'd try out replacing poll(0) to updateAssignmentMetadataIfNeeded as avoiding deprecated method - if it works I'll submit a PR.) I'm feeling that it would be ideal to expose `updateAssignmentMetadataIfNeeded` to the public API, maybe with renaming as `waitForAssignment` which was proposed in KIP-288 if it feels too long. What do you think? If it sounds feasible I'd like to try out contribution on this. I'm new to contribute Kafka community, so not sure it would require a new KIP or not. Thanks, Jungtaek Lim (HeartSaVioR) 1. https://cwiki.apache.org/confluence/display/KAFKA/KIP-288%3A+%5BDISCARDED%5D+Consumer.poll%28%29+timeout+semantic+change+and+new+waitForAssignment+method 2. https://cwiki.apache.org/confluence/display/KAFKA/KIP-266%3A+Fix+consumer+indefinite+blocking+behavior
