@Override
  public void close() {
    if (closed) {
      return;
    }
    // Ensuring that all the segment scanners are closed
    if (heap != null) {
      heap.close();
      // It is safe to do close as no new calls will be made to this scanner.
      heap = null;
    } else {
      for (KeyValueScanner scanner : scanners) {
        scanner.close();
      }
    }
    closed = true;
  }
The MemStoreMergerSegmentsIterator extends MemStoreSegmentsIterator and performs the scan for
simple merge operation meaning it is NOT based on SQM
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreMergerSegmentsIterator.java