@Override
  public void encode(ExtendedCell cell, HFileBlockEncodingContext encodingCtx, DataOutputStream out)
    throws IOException {
    RowIndexEncodingState state = (RowIndexEncodingState) encodingCtx.getEncodingState();
    RowIndexEncoderV1 encoder = state.encoder;
    encoder.write(cell);
  }
Store cells following every row's start offset, so we can binary search to a row's cells. Format:
flat cells integer: number of rows integer: row0's offset integer: row1's offset .... integer:
dataSize
hbase-common/src/main/java/org/apache/hadoop/hbase/io/encoding/RowIndexCodecV1.java