con = ActiveRecord::Base.connection

    # utf8mb4が検証環境のため 65535/4=16383
    length_set = [255, 4096, 16383, :text]
    string_set = [250, 4090, 16380]
    try_count = 10000

    demostr = "123456789A"

    raw_con = con.raw_connection

    Benchmark.bm 40 do |bm|
      length_set.each do |length|
        column_type = length == :text ? "text" : "varchar(#{length})"
        con.execute("create table length_test (str #{column_type})")
        insert_sql = raw_con.prepare("insert into length_test values(?)")
        begin
          string_set.each do |strlen|
            next if length != :text && strlen > length

            insertstr = demostr * (strlen / 10)
            bm.report "#{column_type} <-- string(#{strlen})" do
              try_count.times do
                insert_sql.execute(insertstr)
              end
            end
          end
        ensure
          insert_sql.close
          con.execute('drop table length_test')
        end
      end
    end