From: Roger Pack <rogerpack2005@...>
Date: 2010-05-01T05:22:55+09:00
Subject: Re: File.read(fname) vs. File.read(fname,File.size(fname))

Roger Pack wrote:
>>               user       system     total        real
>> straight read 28.875000  18.032000  46.907000 (  47.812500)
>> read w/ size  0.000000  0.031000  0.031000 (  0.031250)
>> 
>> ...for just a *moderate* 1500x boost in performance.
> ...
>> It appears that the buffer is being grown linearly, giving O(n^2)
>> performance. 

I'm unable to reproduce this except on windows, so that's where you are, 
I assume?

Yeah unfortunately with windows it does exactly what you described 
(except in trunk, where it has been fixed, except still has a bit of 
slowdown when you read files in ascii+translation mode (see last post of 
this thread:
http://www.ruby-forum.com/topic/182875#new)

It does seem that the idea results in some speedup, though:

linux 1.9.2, 500MB file

      user     system      total        real
normal        0.130000   0.810000   0.940000 (  0.938607)
optimized     0.000000   0.740000   0.740000 (  0.749340)

windows 1.9.2, 500MB file

      user     system      total        real
normal        0.250000   0.671000   0.921000 (  0.921829)
optimized     0.000000   0.764000   0.764000 (  0.774697)

plus results in a huge increase in speed for ascii mode in windows.


ruby 1.9.2dev (2010-05-01) [i386-mingw32]
      user     system      total        real
normal         11.342000   0.718000  12.060000 ( 12.735092)
optimized      0.000000    0.437000   0.437000 (  0.446179)


(maybe there is still some N^2 action going on?)

I'll file a feature request for it.

-rp
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