From: "mame (Yusuke Endoh)" <mame@...>
Date: 2012-03-21T23:35:40+09:00
Subject: [ruby-core:43537] [ruby-trunk - Bug #6183][Rejected] Enumerator::Lazy performance issue


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

Status changed from Open to Rejected

Hello,

Enumerator::Lazy is not a silver bullet; it removes the overhead for
creating an intermediate array, but brings the drawback for calling
a block.  Unfortunately, the latter is much bigger than the former.
Thus, in general, Lazy does bring performance drawback.

The worth of Enumerator::Lazy is to extract first some elements from
big array, especially, infinite sequence.  For example:

  Prime.lazy.select {|x| x % 4 == 3 }.take(10).to_a

The code becomes much complex without Lazy:

  a = []
  Prime.each do |x|
    next if x % 4 != 3
    a << x
    break if a.size == 10
  end


Anyway, this is not a bug.  If you have any concrete idea to "fix"
this issue, please reopen the ticket.

Thank you,

-- 
Yusuke Endoh <mame@tsg.ne.jp>
----------------------------------------
Bug #6183: Enumerator::Lazy performance issue
https://bugs.ruby-lang.org/issues/6183#change-25017

Author: gregolsen (Innokenty Mikhailov)
Status: Rejected
Priority: Normal
Assignee: 
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/