private ExtendedCell getRowPrefixCell(ExtendedCell cell) {
    byte[] row = CellUtil.copyRow(cell);
    return ExtendedCellBuilderFactory.create(CellBuilderType.DEEP_COPY)
      .setRow(row, 0, Math.min(prefixLength, row.length)).setType(Cell.Type.Put).build();
  }
@param cell the cell
@return the new cell created by row prefix
hbase-server/src/main/java/org/apache/hadoop/hbase/util/RowPrefixFixedLengthBloomContext.java