From: Kurt Stephens <ks@...>
Date: 2010-03-06T09:31:10+09:00
Subject: [ruby-core:28522] Re: [Feature #905] Add String.new(fixnum) to 	preallocate large buffer

Nikolai Weibull wrote:
> On Fri, Mar 5, 2010 at 17:25, Caleb Clausen <vikkous@gmail.com> wrote:
>> On 3/5/10, Yusuke ENDOH <mame@tsg.ne.jp> wrote:
>>> 2010/3/5 Kornelius Kalnbach <murphy@rubychan.de>:
> 
>>>> How big would the buffer size have to be for this template?
>>>>
>>>>  <p><%= link_to @record.name, @record %></p>

I can guarantee the lower bound of output size of this example is 7.  :p

ERB template rendering is one of my greatest performance issues right now.

I routinely have have ERB templates that are over 80K, comprised mostly 
of large static chunks with a small number of dynamic chunks.

For large templates with small substitutions, the cost of reallocation 
during concatenation is the biggest cost, thus preallocating a String 
buffer to lower bound of the result size of 80k is a big time and memory 
saver.

And I am looking at other template engines (e.g. Erubis).

This is a general problem with String concatenation -- ERB is only one 
of the cases -- consider XML generation.  To top it off, String 
concatentation is slower in MRI > 1.8.6.  String objects provides no 
opportunities to give hints about big they will end up.

Low-level problems deserve low-level solutions.

KAS