formatter_csv: Improve the performance. 2x faster

[repeatedly]

Signed-off-by: Masahiro Nakagawa [email protected]

Which issue(s) this PR fixes:
None

What this PR does / why we need it:
Improve the performance by avoiding creating CSV object per format call.
In ruby 2.6.3, 2x faster than before.

Warming up --------------------------------------
                 now     4.627k i/100ms
                 new     9.692k i/100ms
Calculating -------------------------------------
                 now     49.484k (± 2.1%) i/s -    249.858k in   5.051491s
                 new     98.117k (± 8.4%) i/s -    494.292k in   5.091679s

require 'benchmark/ips'
require 'csv'

class CF
  def initialize
    @fields = ["key1","key2","ke,y3","ke y4","key5","key6","key7","key8"]
    @generate_opts1 = {col_sep: ',', force_quotes: true}
    @generate_opts2 = {col_sep: ',', force_quotes: true, headers: @fields,
                       row_sep: @add_newline ? :auto : "".force_encoding(Encoding::ASCII_8BIT)}

    @cache = {}
  end

  def format1(tag, time, record)
    row = @fields.map do |key|
      record[key]
    end
    line = CSV.generate_line(row, @generate_opts1)
    line.chomp! unless @add_newline
    line
  end

  def format2(tag, time, record)
    csv = (@cache[Thread.current] ||= CSV.new("".force_encoding(Encoding::UTF_8), @generate_opts2))
    line = (csv << record).string.dup
    csv.rewind
    csv.truncate(0)
    line
  end
end

keys = ["key1","key2","ke,y3","ke y4","key5","key6","key7","key8"]
record = {}
keys.each { |key|
  record[key] = "valueeeeee1"
}

cf = CF.new

Benchmark.ips do |x|
  x.report('now') do
    cf.format1(nil, nil, record)
  end

  x.report('new') do
    cf.format2(nil, nil, record)
  end
end

Docs Changes:
No need

Release Note:
Same as title.