title: CURRENT-OFFSET and LAG of kafka consumer group that has no active members
body: <p>How are these two set? Behaviour that I observe with kafka-consumer-groups.sh is that when new message is appended to a certain partition, it increments at first its LOG-END-OFFSET and LAG columns, and after some time, CURRENT-OFFSET column gets incremented and LAG column gets decremented, although no offset was actually commited by any consumer, as there are no active consumers. Am I right, and is this always happening with consumer groups that have no active members, or is there a possibility to turn off the second stage, that simulates commiting offsets by non-existing consumers? This is actually confusing, you have to take into account the information that there are no active members in a consumer group, in order to have the right perspective of what the CURRENT-OFFSET and LAG columns actually mean (not much in that case).</p>
  <p>OK, it seems that the consumer actually does continuously connect and poll the messages and commits the offsets, but in a volatile fashion (disconnecting each time) so that kafka-consumer-groups.sh always reports as if there are no active members in a group.
  This is a flink job that acts this way. Is that possible?</p>