private boolean seekBefore(ExtendedCell seekKey) throws IOException {
    if (seekCount != null) {
      seekCount.increment();
    }
    if (!hfs.seekBefore(seekKey)) {
      this.cur = null;
      return false;
    }

    return true;
  }
This variant of the {@link StoreFileScanner#seekToPreviousRow(ExtendedCell)} method requires
two seeks. It should be used if the cost for seeking is lower i.e. when using a fast seeking
data block encoding like RIV1.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileScanner.java