From: Robert Klemme <shortcutter@...>
Date: 2011-03-16T21:08:42+09:00
Subject: Re: NoMethodError#message takes very long

On Wed, Mar 16, 2011 at 7:24 AM, Eric Hodel <drbrain@segment7.net> wrote:
> On Mar 15, 2011, at 8:25 PM, Adiel Mittmann wrote:
>
>> Hello.
>>
>> I've been noticing a problem for a while in a larger application and today I
>> produced a minimal example, given below. When a method is not found, Sinatra
>> calls NoMethodError#message to display a nice error message, but that is taking
>> VERY long.
>>
>> <snip>
>> require 'sinatra'
>> require 'nokogiri'
>> get '/' do
>>  @xml = Nokogiri::XML(File.new('baz.xml', 'rb').read())
>>  foo()
>>  'hello'
>> end
>> </snip>
>>
>> The file 'baz.xml' can be just a simple file, like a root element containing
>> some thousands of elements. The number of elements is important because, oddly
>> enough, the time taken for the message to be displayed is proportional to the
>> size of the XML file. In my system, with a 3.7 MB file this program takes almost
>> 13 seconds to print the message, but in a larger application the message takes a
>> few minutes to appear.
>
> Let me see if I have this straight:
>
> If baz.xml is empty it is fast
> If baz.xml is large it is slow
>
> If this is true it is because it takes time to parse the XML file before it gets to foo and discovers that there is no method foo.
>
> Ruby does not know that foo does not exist until you try to call it.

Additional remarks: the file is not properly closed and reading the
whole file in one go is probably also not a good solution.  I'd rather

require 'sinatra'
require 'nokogiri'
get '/' do
 @xml = File.open('baz.xml', 'rb') {|io| Nokogiri::XML(io)}
 foo()
 'hello'
end

Note, the fact that you read in a large file as one String can
actually be related to your slowness because it might case GC
overhead.

Cheers

robert

-- 
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