All about Rails - Home

Disabling callbacks in an ActiveRecord data migration

2009-01-29T19:46:00Z

It’s often useful to disable ActiveRecord callbacks such as :after_save when migrating data. It’s rather easy to do:


Foo.after_create.clear
Foo.after_save.clear
... migration code ...

If you only need to disable certain actions, it’s also trivial:


Foo.after_save.reject! {|callback| callback.method.to_s == 'some_method_name' }

This sort of thing should never be used in application code, if you’re doing this then your model is broken. However, it’s great for data migrations.

IRC question of the day

2009-01-09T16:49:00Z

Question:

_adc: I'm doing compiling some reports on various database records based in whatever
 model the user chooses... Is there a better way to figure out which models are in 
existence than http://pastie.org/356630 ?
_adc: I'm looking for an array of all models currently in existence.

Answer:

ActiveRecord::Base.subclasses_of(ActiveRecord::Base)


~/projects/learnhub$ ./script/console 
Loading development environment (Rails 2.1.1)
>> ActiveRecord::Base.subclasses_of(ActiveRecord::Base).collect {|c| c.to_s }
=> ["CGI::Session::ActiveRecordStore::Session", "ContactPostCreationNotification", .....]

Three simple scripts for Passenger (mod_rails) management

2008-12-31T15:00:00Z

Phusion Passenger is the best option for hosting Ruby based web apps (anything that uses Rack is compatible). When used with Ruby EE to serve Ruby on Rails applications it will consume up to 33% less memory than other servers such as Mongrel.

Not everything is kittens and rainbows however, as Passenger won’t prevent your app from choking your server if you consume too much memory (via memory leaks in your app, etc). Schedule this script to run every couple of minutes to kill any Passenger processes are consuming too much memory. Passenger will automatically start new ones as needed. You’ll have to figure out for yourself how much is “too much”. In my case it’s 200 MB.

It’s also useful to know how many process Passenger is using, so you can increase the MaxPoolSize when traffic increases. I use Munin to track system statistics and have written two wrappers around the Passenger system tools. The first wraps passenger-memory-stats and the second wraps passenger-status

The result are graphs such as these:

Munin graphs can be extremely helpful when tracking down system performance issues. I highly recommend it.

TexHub: A math equation service

2008-12-29T19:13:00Z

Carsten and I recently launched TexHub which is a little service for serving up latex equations as images. It’s pretty simple, just Base64 + URI encode latex string and append it to a URL. It’s extracted from our math equations feature on Learnhub

For example:

e=MC²

A more complex example: F(x) = \\int_{-\\infty}{a} f(t)dt + \\int_{a}^{x} f(t)dt

We haven’t done much with the front end yet as we’ll primarily be using it as a service, so the focus has been on speed. I wrote the web interface using Sinatra which turned out to be perfect for this sort of app. I plan on writing more micro apps in the future with Sinatra, perhaps the next thing will be the Ruby version of Tilomino which has been sitting untouched for two years….

Irony

2008-08-25T21:45:00Z

Glad to know that MS still considers that IE 6.0 is a ‘recent browser’ (it’s 7 years old, which is ancient in internet years).

Ruby VM shootout on Rock, Paper, Scissors!

2008-08-11T19:19:00Z

Update: I’ve added benchmark numbers for JRuby 1.1.3

I’ve been messing with RubyRPS (Rock, paper scissors) lately, it’s a ton of fun! I thought it might be cool to benchmark the progression of Rubinius, and that little experiment turned into a full blown ruby interpreter shootout. Sure, this is hardly fair since RPS doesn’t use much in the way of complicated stuff (lots of loops over array, etc), but most benchmarks are bullshit anyways. I just want my RPS bots to run fast!

Here are the versions I tested.

ruby 1.8.6 (2008-03-03 patchlevel 114) [universal-darwin9.0] (macports)
ruby 1.8.7 (2008-06-20 patchlevel 22) [i686-darwin9.3.0] (macports)
ruby 1.9.0 (2008-03-01 revision 15664) [i686-darwin9.4.0] (macports)
ruby 1.9.0 (2008-07-25 revision 18218) [i686-darwin9.4.0] (snapshot 1.9.0.3)
Rubinius 0.9.0 (ruby 1.8.6 compatible) (ffb998bf5) (08/07/2008) [i686-apple-darwin9.4.0] (from trunk)
JRuby 1.8.6 (2008-08-07 rev 6555) [i386-jruby1.1.1] (macports)
MacRuby version 0.3 (ruby 1.9.0 2008-06-03) [universal-darwin9.4] (downloaded binary)

Benchmarking is rather simple:


# time ruby ./run.rb
# time ruby1.8.7 ./run.rb
# time ruby 1.9 ./run.rb
# time rubinius ./run.rb
# time jruby ./run.rb
# time macruby ./run.rb

Interpreter	Memory Usage	Real	User	System
Ruby 1.8.6	3MB	0m36.183s	0m35.426s	0m0.241s
Ruby 1.8.7	10MB	0m17.778s	0m17.086s	0m0.154s
Ruby 1.9.0	11MB	1m17.092s	0m53.843s	0m22.234s
Ruby 1.9.0.3	10MB	0m10.350s	0m9.911s	0m0.111s
JRuby 1.1.1	28MB	0m18.023s	0m16.198s	0m0.417s
JRuby 1.1.3	28MB	0m18.622s	0m17.482s	0m0.321s
Rubinius	26MB	0m42.836s	0m41.556s	0m0.479s
MacRuby 0.3	476MB	0m42.471s	0m40.302s	0m0.987s

How about a threaded run just for fun?


# time ruby ./run.rb --threaded
# time ruby1.8.7 ./run.rb --threaded
# time ruby 1.9 ./run.rb --threaded
# time rubinius ./run.rb --threaded
# time jruby ./run.rb --threaded
# time macruby ./run.rb --threaded

Interpreter	Memory Usage	Real	User	System
Ruby 1.8.6	4MB	1m12.343s	1m9.703s	0m0.695s
Ruby 1.8.7	13MB	0m18.019s	0m17.561s	0m0.188s
Ruby 1.9	13MB	1m18.341s	0m54.516s	0m21.947s
Ruby 1.9.0.3	13MB	0m10.505s	0m10.013s	0m0.126s
JRuby 1.1.1	34MB	0m17.048s	0m22.013s	0m1.890s
JRuby 1.1.3	31MB	0m15.630s	0m22.580s	0m1.475s
Rubinus	52MB	0m43.745s	0m41.893s	0m0.591s
MacRuby 0.3	Error!	stack level too deep (SystemStackError)

Conclusion

Ruby 1.9 runs RPS really fast. You may have to compile it yourself for now if you’re on a Mac, since the version in Macports does have some issues. Also, I’d recommend that anyone who is still running Rails apps on 1.8.6 to move to 1.8.7 to for an increase in speed. We’ve been using 1.8.7 to run Learnhub for a few weeks now and have noticed a decrease in memory leaks as well. Be sure to check for compatibility with your Rails app though, 1.8.7 doesn’t work with some older versions of Rails.

Surprises

I was surprised that Jruby did so well. It performs just as well as MRI 1.8.7 (with about double the memory usage). I was expecting the interpreter startup time to hold Jruby back, but that didn’t turn out to be the case. Rubinius also performed a bit better than expected (they’ve been working on correctness rather than speed thus far). It wasn’t much slower than MRI 1.8.6, although it consumed far more RAM. My understanding is that the VM is currently being rewritten, so I’ll run a few more tests when it’s released.

MacRuby is also an interesting project, with a goal of porting MRI 1.9 to run directly on top of Mac OS X core technologies such as the Objective-C common runtime and garbage collector, and the CoreFoundation framework. It’s very much a work in progress at this point.

Microsoft Doesn't Care About the Web

2008-08-06T05:45:00Z

I just wanted to read some comments on a MSN Money article. I got this:

Microsoft FAIL.

acts_as_paranoid and counter_cache

2008-07-28T01:40:00Z

Counter caches in RoR eliminate the need to issue an sql query to determine the size of an associated collection. Using counter cache is quite simple. Here’s an example:


class Author < ActiveRecord::Base
  has_many :books
end

class Book < ActiveRecord::Base
  belongs_to :author, :counter_cache => true
end

add_column :authors, :books_count, :integer

Author.first.books.count  # gets the value from the books_count column, 
                              # rather than doing an sql count

There’s a problem if you use this alongside acts_as_paranoid. AAP is a plugin that provides ‘soft delete’ functionality. In order to achieve this, AAP overrides AR finder methods to check the ‘deleted_at’ column to determine if a record has been ‘deleted’. Due to a condition placed on the count (counting only undeleted objects), the counter cache is not used and instead an sql statement is issued.


class Author < ActiveRecord::Base
  has_many :books
end

class Book < ActiveRecord::Base
  acts_as_paranoid
  belongs_to :author, :counter_cache => true
end

Author.first.books.count # SELECT count(*) AS count_all FROM `books` 
                             # WHERE (`books`.author_id = 11524) AND 
                             # (`books`.deleted_at IS NULL OR 
                             # `books`.deleted_at > '2008-07-27 13:27:22')

Deleting an object from a ‘paranoid’ collection will still do the right thing (decrement the counter cache), making this easy to fix. You just have to add your own count method for the collection.


class Author < ActiveRecord::Base
  has_many :books do
    def count
       books_count
    end
  end
end

Author.first.books.count  # calls the count method, returning
                       # the books counter

This is also published on Learnhub

Nginx + HaProxy gotcha

2008-07-22T23:16:00Z

I’ve recently switched from using a straight up Apache mod_proxy + mongrel setup to Nginx + HaProxy +mongrel. Basically, mod_proxy is dumb as shit, and should never be used with mongrel + rails, especially with better options like Passenger and HaProxy.

Why does mod_proxy suck? Take a look for yourself:


[8030/5/247]: handling 127.0.0.1: GET
[8031/6/134]: handling 127.0.0.1: GET
[8032/2/160]: handling 127.0.0.1: GET
[8033/0/93]: idle
[8034/10/128]: handling 127.0.0.1: GET
[8036/2/124]: handling 127.0.0.1: GET
[8035/0/110]: idle
[8037/0/101]: idle

Look at this garbage. There are three idle mongrels even though the other five have 25 requests to be processed.

Whats great about HaProxy is that it will queue up requests and only distribute them to idle mongrels. It translates into way better response times under load. Add Nginx, which is way easier to configure that Apache, allowing me to easily setup things like sending known ‘slow’ requests to separate mongrels and it’s a big win. As a bonus, haproxy has a great status tool, which gives a quick overview of your proxy clusters.

One little problem …

The gotcha when I initially switched over was that exception_notifier stopped sending me error emails, in fact the errors were being displayed to the user. What the hell?

Exception notifier looks at the incoming IP address. If it’s local (aka: 127.0.0.1), it’s assumed that the user is a developer, so it won’t email the exception to you. haproxy was sending nginx’s IP address, rather than the forwarded client address. The problem was that I had configured both nginx and haproxy to forward headers.

haproxy.conf:


option          forwardfor    # enable insert of X-Forwarded-For headers

nginx.conf


proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;

Removing the header forwarding in the haproxy configuration solved the problem. You only need to set the X-Forwarded header in Nginx (or Apache or Pound or whatever front end you choose). Setting it in Haproxy as well will over write the header with one containing the IP of the front end. Since I have Nginx and Haproxy running on the same machine, that IP is 127.0.0.1, which broke the exception_notifier.

This is also published on Learnhub

Ruby Fringe

2008-07-21T05:18:00Z

Ruby Fringe wrapped up today and it was incredible. All of the presentations were compelling, the food was great and the parties were tons of fun. I met a ton of interesting people (who are way smarter than me), and find myself exhausted and happy.

Congratulations goes out to Pete, Meghann and the rest of the Unspace for pulling together such a great event.

Upgrading non-trivial apps to Rails 2.1

2008-06-25T16:19:00Z

I finished updating Learnhub to run on Rails 2.1. I wrote an article about a few things I learned along the way: Upgrading non-trivial apps to Rails 2.1

Microsoft Office Protocol Discovery is annoying

2008-06-12T15:50:00Z

If you’re getting annoying exception notifications, generated by a client named “Microsoft Office Protocol Discovery”, or even “Microsoft Data Access Internet Publishing Provider Protocol Discovery” this will help.

http://rails.learnhub.com/lesson/page/2329-dealing-with-microsoft-office-protocol-discovery-in-railsv

Fun with Learnhub

2008-06-11T17:15:00Z

We finally have launched the new Learnhub homepage after spending a lot of effort on it. It looks great!

Also, TechCrunch posted a positive article on Learnhub Check it out!

Railsconf 08 on video

2008-06-04T01:55:00Z

There were some great interviews recorded at Railsconf, and Rails Envy release some new videos. Here they are:

Session Store Switching

2008-05-21T16:38:00Z

I wrote a short article about a little gotcha, and the solution to it when switching your rails session store. Check it out: http://rails.learnhub.com/lesson/page/1858-how-to-switch-your-default-session-store