You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: populate-file-info-columns-in-collections.rb
    path of file: ./repos/arvados/services/api/script
    
    the code of the file until where you have to start completion: #!/usr/bin/env ruby
# Copyright (C) The Arvados Authors. All rights reserved.
#
# SPDX-License-Identifier: AGPL-3.0

# Arvados version 1.4.0 introduces two new columns
    
def main

  distinct_pdh_count = ActiveRecord::Base.connection.exec_query(
    "SELECT DISTINCT portable_data_hash FROM collections where file_count=0"
  ).rows.count

  # Generator that queries for all the distinct pdhs greater than last_pdh
  ordered_pdh_query = lambda { |last_pdh, &block|
    pdhs = ActiveRecord::Base.connection.exec_query(
      "SELECT DISTINCT portable_data_hash FROM collections "\
      "WHERE file_count=0 and portable_data_hash > '#{last_pdh}' "\
      "ORDER BY portable_data_hash LIMIT 1000"
    )
    pdhs.rows.each do |row|
      block.call(row[0])
    end
  }

  batch_size_max = 1 << 28 # 256 MiB
  GroupPdhs.group_pdhs_for_multiple_transactions(ordered_pdh_query,
                                                 distinct_pdh_count,
                                                 batch_size_max,
                                                 "AddFileInfoToCollection") do |pdhs|
    do_batch(pdhs)
  end
end