ruby on rails - extremely slow csv exporting -

we trying generate csv file users download. however, it's extremely slow, 5 minutes 10k lines of csv.

any idea on improving? code below:

def download_data   start_date, end_date = get_start_end_date   report_lines = @report.report_lines.where("report_time between (?) , (?)", start_date, end_date)    csv_string = csv.generate |csv|     report_lines.each |report_data|       csv << [report_data.time, report_data.name, report_data.value]     end   end    respond_to |format|     format.csv { send_data(csv_string, :filename => "#{time.now}.csv", :type => "text/csv") }   end end 

i start checking if report_time indexed, unindexed report_time going contribute slowness. refer active record migration details on adding index.

second, trim down result need, i.e. instead of selecting columns, select time, name, , value:

report_lines = @report.report_lines                       .where("report_time between (?) , (?)", start_date, end_date)                       .select('time, name, value') 

try with:

def download_data   start_date, end_date = get_start_end_date   report_lines = @report.report_lines.where("report_time between (?) , (?)", start_date, end_date).select('time, name, value')    csv_string = csv.generate |csv|     report_lines.map { |row| csv << row }   end    respond_to |format|     format.csv { send_data(csv_string, :filename => "#{time.now}.csv", :type => "text/csv") }   end end