Bug #17478


Ruby3.0 is slower than Ruby2.7.2 when parsing a large CSV file

Added by okkez (okkez _) about 3 years ago. Updated 6 months ago.

Target version:
ruby -v:
ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-linux]


Ruby3.0 is around 10%-20% slower than Ruby2.7.2 when parsing and aggregating a large CSV file.

The script is here:

require "csv"

name_to_cost =

CSV.foreach(ARGV[0], headers: true) do |row|
  name_to_cost[row["name"]] += row["cost"].to_f

name_to_cost.sort_by {|k, _| k }.each do |name, cost|
  printf "%s\t%.3f\n", name, cost

The sample data is like following(3 mega lines and the size is about 235MiB):

2365599605,ysgHDPA,Voluptatem sit perferendis accusantium consequatur aut.,25.115
2365599606,xFLXOtJ,Sit accusantium aut perferendis voluptatem consequatur.,60.228
2365599607,RlkxNQB,Accusantium sit aut consequatur perferendis voluptatem.,79.663
2365599608,YVMbuva,Sit perferendis voluptatem accusantium aut consequatur.,49.863
2365599609,rtxVcDW,Accusantium voluptatem sit perferendis aut consequatur.,50.765
2365599610,rtxVcDW,Aut sit accusantium consequatur perferendis voluptatem.,94.310
2365599611,muDwuke,Consequatur sit accusantium aut perferendis voluptatem.,16.991
2365599612,tkqFWyM,Perferendis sit voluptatem consequatur aut accusantium.,98.753
  • Ruby2.7.2: 25.37 seconds
  • Ruby3.0.0: 27.53 seconds

I use this program to generate the test CSV file:

In case of using another private data:

  • Ruby2.7.2: 31.54 seconds
  • Ruby3.0.0: 37.15 seconds

The private data is like followings:

  • There are 18 columns
  • There are 1144305 lines
  • It is 334MiB

Updated by hsbt (Hiroshi SHIBATA) over 2 years ago

  • Status changed from Open to Assigned
  • Assignee set to kou (Kouhei Sutou)

Updated by jeremyevans0 (Jeremy Evans) 6 months ago

  • Status changed from Assigned to Closed

I did some testing with the CSV example given in the original post repeated 400k times. Note that Ruby 2.7 ships with CSV 3.1.2 and Ruby 3.2 ships with CSV 3.2.6.

  • 2.7: 49 seconds
  • 3.2: 77 seconds
  • 3.2 --yjit: 59 seconds
  • 3.2 with CSV 3.1.2: 48 seconds
  • 3.2 --yjit with CSV 3.1.2: 33 seconds

Since the performance issue is in the csv library, and not in Ruby itself, I'm closing this.

You may want to bisect changes to the csv library between 3.1.2 and 3.2.6, and if you identify an unnecessary performance regression, file an issue upstream: . Alternatively, just use CSV 3.1.2 if performance is an issue and you don't need features added since.


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