title: Why kafka consumer (0.10.0.0) for new consumer group does see old/previously published messages?
body: <p>I have a producer that publishes messages on a topic called 'mytopic' just fine. I have 2 consumers in 2 different consumer groups listening for these messages. I started these 2 consumers and producer in following sequence.</p>
  
  <p>1) Start consumer 1 in group 'group1'
  2) start producer to publish several hundreds messages</p>
  
  <p>After sometime I check the offset of consumer 1, which is as I expect:</p>
  
  <p><code>/opt/kafka_2.11-0.10.0.0/bin/kafka-consumer-offset-checker.sh --zookeeper localhost:2181 --topic mytopic --group group1</code></p>
  
  <p>Output:</p>
  
  <p><code>Group           Topic                          Pid Offset          logSize         Lag             Owner
  group1           mytopic                         0   30230           36942           6712            none</code></p>
  
  <p>3) Now I start consumer 2 in group 'group2' to listen to the same messages but it comes back with 0 messages on every poll() call.
  The offset check for this consumer shows me that its offset is same as the logSize.</p>
  
  <p><code>/opt/kafka_2.11-0.10.0.0/bin/kafka-consumer-offset-checker.sh --zookeeper localhost:2181 --topic mytopic --group group2</code></p>
  
  <p>Output:
  <code>Group           Topic                          Pid Offset          logSize         Lag             Owner
  group2           mytopic                         0   36942           36942           0               none</code></p>
  
  <p>Same problem for any other consumer with a new consumer group. Why is the consumer joining a new consumer group after messages have been published not seeing the old messages even though messages exists on the topic (ie., haven't been deleted)?</p>