public String getUpcomingOffset() {
      return upcomingOffset;
    }
@return The offset that represents the next message to be written in the
        stream for the partition given. If a partition has two messages
        with offsets 0 and 1, respectively, then this method would return
        2 for the upcoming offset. This offset is useful when one wishes
        to pick up reading at the very end of a stream. A null value
        means the stream is empty.
samza-api/src/main/java/org/apache/samza/system/SystemStreamMetadata.java