gistfile1.rb

REV[1]
require 'json/ext'

batch_size = 1000
fields = ["id", "priority", "attempts", "handler", "last_error", "run_at", "locked_at", "failed_at", "locked_by", "created_at", "updated_at"]

ActiveRecord::Base.connection.execute("SELECT COUNT(*) FROM delayed_jobs;").each { |x| @total_rows = x[0] }

File.open("tmp/delayed_jobs.json","w") do |f|
  ((@total_rows / batch_size)+1).times do |i|
    ActiveRecord::Base.connection.execute("SELECT * FROM delayed_jobs LIMIT #{batch_size} OFFSET #{(1000 * (i+1)}").each do |row|
      hsh = {}
      fields.each_with_index do |field, index|
        hsh.merge!(field.to_sym => @row[index])
      end
      f.write(JSON.generate(hsh))
    end
  end
end

REV[2]
require 'json/ext'

batch_size = 1000
fields = ["id", "priority", "attempts", "handler", "last_error", "run_at", "failed_at", "created_at", "updated_at"]

total_rows = ActiveRecord::Base.connection.select_value("SELECT COUNT(*) FROM delayed_jobs;")

File.open("tmp/delayed_jobs.json","w") do |f|
  ((total_rows / batch_size)+1).times do |i|
    ActiveRecord::Base.connection.select_rows("SELECT #{fields.join(',')} FROM delayed_jobs LIMIT #{batch_size} OFFSET #{(1000 * (i+1)}").each do |row|
      hsh = {}
      fields.each_with_index do |field, index|
        hsh.merge!(field.to_sym => @row[index])
      end
      f.write(JSON.generate(hsh))
    end
  end
end

You can do the count with connection.select_value instead.

Also, you don't need to store locked_at and locked_by.

For the second execute, I think you should connection.select_rows instead.