From: Jano Svitok <jan.svitok@...>
Date: 2007-08-14T03:57:13+09:00
Subject: Re: Why don't Ruby libraries share memory?

On 8/13/07, Matt Harvey <matt@teamdawg.org> wrote:
> This paragraph is motivation. While my question is not Rails-specific, I am
> asking it because of Rails. I've been investigating the memory footprint of
> my Mongrels. It is nice that they share the .so libraries from ImageMagick
> as well as other C libraries. However, each one still has about 20MB in
> [heap]. My theory is that a lot of this is coming from ActiveRecord and
> friends getting loaded again and again for each Mongrel, which seems to me
> entirely unnecessary. My "marginal cost of Apache" is 1376kB. My "marginal
> cost of Mongrel" is 27528kB, with the code I wrote. It seems that the latter
> could be reduced a lot by sharing some Ruby libraries.
>
> The question is as follows: if I require 'library' in one instance of Ruby
> and then require 'library' again in another instance of Ruby, then do I get
> duplicate copies of library's code in two chunks of my RAM? (I'm thinking I
> do.) Why?

I suppose the main problem is that Rails (or ActiveRecord, I don't
know exactly) is not thread-safe. That means you cannot share most of
its the data. That is the reason why you have to run more mongrels
compared to a one multi-threaded mongrel.

I don't know where exactly is the problem with rails/ar though, nor
whether is it at least theoretically solvable.