default long getScannerOrder() {
    return 0;
  }
Get the order of this KeyValueScanner. This is only relevant for StoreFileScanners. This is
required for comparing multiple files to find out which one has the latest data.
StoreFileScanners are ordered from 0 (oldest) to newest in increasing order.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/KeyValueScanner.java