From: "mame (Yusuke Endoh)" <mame@...>
Date: 2012-04-03T18:29:17+09:00
Subject: [ruby-core:44106] [ruby-trunk - Bug #6183] Enumerator::Lazy performance issue


Issue #6183 has been updated by mame (Yusuke Endoh).


Hello,

matz (Yukihiro Matsumoto) wrote:
> Nobu, could you review the patch?  And if you don't see any problem, check it in?

I didn't read the patch, but I found a weird behavior.
I think the approach is interesting, though.

  $ cat t.rb
  a = (1..10).lazy
  p a.map {|x| x + 1 }.to_a
  p a.map {|x| x + 1 }.to_a
  p a.map {|x| x + 1 }.to_a

  # without the patch
  $ ./miniruby.org t.rb
  [2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
  [2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
  [2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

  # with the patch applied
  $ ./miniruby.new t.rb
  [2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
  [3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
  [4, 5, 6, 7, 8, 9, 10, 11, 12, 13]

-- 
Yusuke Endoh <mame@tsg.ne.jp>
----------------------------------------
Bug #6183: Enumerator::Lazy performance issue
https://bugs.ruby-lang.org/issues/6183#change-25633

Author: gregolsen (Innokenty Mikhailov)
Status: Assigned
Priority: Low
Assignee: nobu (Nobuyoshi Nakada)
Category: 
Target version: 
ruby -v: ruby 2.0.0dev (2012-03-17 trunk 35075) [x86_64-linux]


I benchmarked Enumerator::Lazy and that's what I got:
                 user     system      total        real
Lazy:        0.690000   0.010000   0.700000 (  0.733160)
Normal:      0.160000   0.010000   0.170000 (  0.186695)

It seems like even with 4 chain links and 3000 elements in initial array, Lazy enumerator is almost 4(!) times slower than the normal case.

Instead of performance benefit we've got 4 times performance drawback.

See test file attached.


-- 
http://bugs.ruby-lang.org/