From: Jano Svitok <jan.svitok@...>
Date: 2007-11-17T23:13:07+09:00
Subject: Re: REXML memory consumption

On Nov 17, 2007 7:58 AM, Ray Chen <ray.c.chen@gmail.com> wrote:
> My process memory usage has been increasing steadily, and some probing
> pointed me to REXML.  I created a test that consisted of feeding 10 xml
> files ranging in size from 15kB to 270kB to REXML::Document.new().  The
> files are fed smallest to largest.  I would think that memory usage
> should return back to ~8 MB since the REXML::Document should go out of
> scope, and everything should get garbage-collected.
>
> Is there something wrong with my understanding of Ruby or does REXML
> hold onto memory?

You can get marginally better by replacing
>   #create the string
>   f = File.open("/tmp/#{i}.xml", 'r')
>   str = ''
>
>   while line = f.gets
>     str << line
>   end
>   f.close

with

str = File.read("/tmp/#{i}.xml")

NB: The your version would be better written (with regards to
exception safety etc.) as:

str = ''
File.open("/tmp/#{i}.xml", 'r') do |f|
  while line = f.gets
    str << line
  end
end

>   #construct the xml
>   xml = REXML::Document.new(str)
>   xml = nil
>
>   return nil
> end

As Robert said, there are more things happening. One of them is that
ruby allocates memory in increasing heap blocks.
If anything used is still inside the block, the block won't be
released to system.

I tried to reuse one string as a buffer for the file, but it didn't
help [see IO#read(lenght, buffer)]. Other thing I tried was to
send the file itself to REXML::Document.new, but it was even worse [
File.open(...) {|f| REXML::Doc.new(f) }].

This is on win xp sp2.

You can find on the net some tools to find out what consumes the
memory - but most of them are in the
hacks category (no offense!). On windows there is the Ruby Memory
Validator that does a similar job.