@Override
  public String toString() {
    String res = "Store segment scanner of type " + this.getClass().getName() + "; ";
    res += "Scanner order " + getScannerOrder() + "; ";
    res += getSegment().toString();
    return res;
  }
Called after a batch of rows scanned (RPC) and set to be returned to client. Any in between
cleanup can be done here. Nothing to be done for MutableCellSetSegmentScanner.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/SegmentScanner.java