title: How does subscriber in IBM MQ pub/sub system knows it has received all messages of the day?
body: <p>Every night a system on IBM Mainframe puts around 50k messages on a DB2 table and tells a Java service when it can start processing.</p>
  <p>This java service is part of a pub/sub system and publishes all these messages on IBM MQ at once.</p>
  <p>An AS400 subscriber pulls these messages from queue (in random order). This system wants to start their night processing, after it has accumulated all these messages. So the subscriber needs to know the moment when it can start further processing (when it has received all these messages).</p>
  <p>How does one generally accomplish this? (taken into account the random order of processing the messages)</p>