From: Giles Bowkett <gilesb@...>
Date: 2006-11-29T10:16:22+09:00
Subject: Re: Two Advanced Ruby Performance Questions

Hey Ezra, this is an awesome e-mail, are you going to blog it? Can I?
I just forwarded it to a client, and I would have sounded much more
intelligent in a phone interview the other day if I'd had this
knowledge at my disposal then. This is the most useful thing I've read
on Rails scaling in a while.

-- 
Giles Bowkett
http://www.gilesgoatboy.org
http://gilesbowkett.blogspot.com


On 11/27/06, Ezra Zygmuntowicz <ezmobius@gmail.com> wrote:
> Hello Sunny-
>
> On Nov 26, 2006, at 1:10 PM, Sunny Hirai wrote:
>
> > First, I am a Ruby newbie but am an experienced developer of highly
> > scalable applications.
> > <snip>
> >
> > QUESTION 1
> >
> > Is there a way (or does it do this already) for the Classes of the
> > application to be cached such that it doesn't add performance
> > overhead?
> > Because it is such a dynamic language, my understanding is that the
> > classes themselves are created at run-time and DO add overhead before
> > any object instantiation occurs. My guess is that this would still
> > happen under YARV too?
> >
> > In other words, can I create a scope in the web application (say a
> > scope
> > that lasts the lifetime of the web server) where I can store class
> > definitions and/or object instances themselves and then use them to
> > create instances in the page request scope?
> >
> > Why I want to do this is so I can define many classes without
> > having to
> > worry about the overhead of having them defined at runtime for every
> > page request. In this way, if I don't use the classes in a page
> > request,
> > they won't add any extra to the execution time.
> >
> > When I write Javascript, I know that there is overhead so I have to
> > keep
> > my libraries short and sweet. In ColdFusion, I have created a
> > framework
> > that stores shared classes and object instances in what ColdFusion
> > calls
> > an "application" scope so that classes and objects are setup only once
> > at application startup (my framework is a little more complex than
> > this
> > but you probably get the point). Because of this, I have many
> > libraries
> > and they are wide and deep. This is very helpful because I can create
> > many helper libraries without worrying about performance overhead.
> >
> > I want to know if this is possible in Ruby.
>
> Yes this is entirely possible in ruby. You can easily pre load all
> classes at server start time inastead of per request once you are
> ready for production environment. What I mean is that in a
> development mode it is very handy to have classes reload for every
> request. This allows you to make code changes and see them instantly
> reflected in the browser. But this is only good for when you are
> developing your applications. When you no longer are making changes
> to the source code then you can pre load all classes and not reload
> them per request. This does reduce the overhead for apps in
> production quite a bit but still can allow you to do dev in an easy
> way as well.
> >
> > Overall, I'm not really sure what kind of persistence and
> > non-persistence there is between page requests when Ruby is attached a
> > web server.
>
> This is entirely up to you. In something like rails you have the
> session around for state between requests. But you can also run a drb
> (distributed ruby) daemon to do longer tasks in an asyncronous way to
> increase speed. In effect offload any time consuming tasks to a
> background daemon and let the htp request return right away thru an
> xmlhttprequest. Then polling to check the status of jobs. These
> daemons can be avaiable to all your ruby processes running your
> application code.
>
> The best way to obtain high throughput in ruby web applications is to
> add more processes behind a http or fcgi proxy. This is how rails and
> other frameworks scale. You add more processes to the cluster and
> they share state through the database or other means like memcached
> or drb.
>
> >
> > Any thoughts or pointers to resources would be helpful.
> >
> > QUESTION 2
> >
> > I've found a lot of documentation on ERB but a lot less on eRuby. All
> > the documentation I have found on eRuby has it executing from the
> > command line or through a web server plugin, usually through
> > Apache. Can
> > eRuby be called from inside Ruby to do parsing? I ask this because
> > eRuby
> > seems like it would execute faster seeing it is built using C.
> >
> > Using ERB is straightforward but I'd love to get the performance
> > benefits of using eRuby if I could; however, my framework would likely
> > requiring making calls from inside Ruby and not ONLY .rhtml files
> > directly.
> >
> > I'm guessing we can use ERB to generate the Ruby code and saving the
> > generated code to a file and then executing the generated file. This
> > would improve performance since the parsing step only happens once;
> > however, I'd still like to know if eRuby can be used this way.
>
>
> Ok this you are going to like. There is a erb compatible alternative
> that is 3 times faster then ERB and 10-15% faster then the C eruby
> and it is written in pure ruby. Its called erubis:
>
> http://www.kuwata-lab.com/erubis/
>
> I also want to mention a project I am working on. Its called Merb
> mongrel+erb:
>
> http://merb.devjavu.com/
> http://svn.devjavu.com/merb/README
>
> Merb is faster lightweight replacement for ActionPack which is the VC
> layer for the rails MVC. Merb still uses ActiveRecord for database
> persistence. But it can also use Og or Mongoose(pure ruby db). It is
> integrated into mongrel for http serving and has its own controller
> and view abstraction with sessions filters and erb. It is just a lot
> smaller and closer to the metal then ActionPack. I wrote it mainly to
> use in conjusnction with rails applications. To have a small merb app
> stand in for performance sensative portions of an application.
>
> ActionPack is not thread safe and requires a  mutex around the entire
> dispatch to rails. This can cause problems with file uploads. Because
> each file upload blocks an entire rails app server for the duration
> of the upload. This means that if you have numerous users uploading
> large files all at once, you will need an app server instance for
> each concurrent upload(!). This was one of the original reasons I
> made merb. It has its own mime parser and does not use cgi.rb or
> anything else that makes actionpack non thread safe. So it can
> process many concurrent file uploads or requests at one time in one
> multi threaded app server mongrel process. Merb does use a mutex for
> parts of the request that can be calling out to ActiveRecord code
> because although ActiveRecord is thread safe, it does not perform
> better then single threaded mode and does cause some other problems.
> So all of the header and mime parsing is handled in thread safe
> sections of the code and only uses a mutex for sections of code that
> call the database. ActionPack has a mutex around all mime body
> parsing as well as everything else actionpack does to serve one request.
>
> You mention you would rather build most of your own framework to be
> closer to the metal. But you may want to look at merb and see if you
> want to work on it with me. I plan on continuing its development and
> it is being used in heavy production already. Augmenting rails
> applications for faster response times and file uploads.
>
> >
> > FINAL COMMENTS
> >
> > Sorry for the monster large post. This is incredibly important for us
> > and will help us decide if we want to switch to Ruby for our new
> > application. We have a large amount of good code in ColdFusion but
> > as an
> > agile company, I can see the benefits of Ruby down the line,
> > especially
> > after a couple of years. Mostly, I love the clean syntax and the
> > overall
> > design of the language.
> >
> > Thanks for your input and I hope (beg) that somebody can help answer
> > these questions.
>
> I also find that Xen virtualization works very well for scaling ruby
> applications. Scaling ruby apps usually means adding more application
> servers and maxing out your database servers. Also caching plays an
> important role as well. Anything that can be cached to static files
> or even partial caching or using memcached for expensive sections of
> code can yield big performance gains. Using a number of Xen virtual
> machines with a shared filesystem like gfs can make it easy to scale
> your ruby applications pretty much horizontally. You just end up
> pushing the persistence into the database, memcached or drb and
> trying to use the "shared nothing" approach for as many portions of
> the system as you can.
>
> In an application stack like this adding nodes to the app server
> cluster is easy and gives you very good scalability up or down. Ruby
> is really a small part of a technology stack like this. There are
> lots of other places to optimize performance. We have built a custom
> Gentoo distribution that is tailored to running ruby application at
> optimal performance in Xen instances. I hope to release this distro
> as soon as I get some free time to package it up.
>
> Cheers-
>
> -- Ezra Zygmuntowicz
> -- Lead Rails Evangelist
> -- ez@engineyard.com
> -- Engine Yard, Serious Rails Hosting
> -- (866) 518-YARD (9273)
>
>
>
>