Detached being

Rails, Sessions, Memcached and Uptime

2011-06-09T19:24:00.003+02:00

Imagine you have a big Rails app. Like really big. With data center load balancer forwarding requests to your boxes. Then on each box you have a load balancer forwarding requests to your rails dispatchers. That's big enough.

Usual approach to keep things running and what's more important - to get notified when things break is to have a load balancer sending a request to something like /uptime/check.

Awesome thing about rails projects is that usually uptime controller looks like this:


class UptimeController < ApplicationController
  def check
    render :text => 'up!', :layout => false
  end
end

Simple enough huh? Well not really because awesome thing about big projects is that your application controller looks a bit like that:


class ApplicationController < ActionController::Base
  before_filter :filter_1, :filter_2, ..., :filter_1000
end

And with 99% certainty i can say that one of filters is doing the following:


def login_from_session
  @current_user = User.find_by_id(session[:user_id])
end

So essentially every request from your load balancer will generate a memcache miss and then memcache write and one session that is never used again. Do we need it? No. Solution? skip_before_filter. Solved? No!

Easier solution will be to extend your UptimeController not from ApplicationController but from ActionController::Base. Who said you can't do it? You can. It's better because you never know when will somebody create another before filter that will try to access session and mess up everything again. What are the benefits? Less code, more maintainable code, better performing code.

/etc/.git

2008-12-06T14:53:00.004+01:00

I just had that great idea to put my /etc folder into git repository and it looks like some other great guys also had this great idea.

All credits to TopperH - his post saved me a lot of bashing :)

Reversing binary in Erlang

2008-11-23T12:52:00.003+01:00

It's weird but erlang does not have any BIF for reversing binary so i tried to write the function and there were two options:

list_to_binary(lists:reverse(binary_to_list(B)))

writing own loop for reversing

loop function worked better than list_to_binary but then i thought what would be faster: looping binary by one byte(:8) nor looping it by word(:16)? well word was faster. then obviously i decided to check it with size :32, :64 and :128. In the end fastest solution was like this:


reverse(B) ->
  S = size(B)*8,
  <<i:s/integer-big>> = B,
  <<i:s/integer-little>>.

But when binary is bigger than bigint can handle(around 2MB) function becomes much more trickier.

Build Erlang on Ubuntu

2008-08-26T13:43:00.002+02:00

Long story short.

I cloned git repo of erlang-otp here: http://github.com/mfoemmel/erlang-otp and tried to ./configure && make && sudo make install but instead of fancy new erlang i got error ~ "can't write file" somewhere in hipe folder.

to build succesfully i had to

mm@mm-desktop:~/dev/git/erlang-otp/lib/hipe$ mkdir ebin
mm@mm-desktop:~/dev/git/erlang-otp/lib/common_test/priv$ mkdir lib

happy compiling

Talk to the clouds

2008-06-03T08:19:00.000+02:00

Instant messaging with friends is past. Future is instant messaging with computers.

Take a look at theese slides introduced by Ezra:

| View | Upload your own

Why use distributed SCM?

2008-05-30T17:08:00.000+02:00

So why would you switch from centralized SCM to distributed SCM?

well here's the first argument:

Due to errors in our backup scripts, we have gone two weeks without backups of the repositories. Unfortunately, we made an error when cleaning our filesystems. As a result, some repositories have been deleted. Some of them have been recovered from our last backup, which we regret is two weeks old. If you can't access your repository, mostly likely it is lost. We sincerely apologize for any loss of data and inconvenience.

https://opensvn.csie.org/

Firefox 3. Significant.

2008-04-07T08:31:00.000+02:00

So it's significant. Really.
Javascript performance is up to 5 times faster than Firefox 2 and I don't even compare to IE crap.

Here's SunSpider results

Firefox 3 Beta 5

Firefox 2.0.11

I hope AdblockPlus guys will update their addon because I do not plan to use Firefox 2 except for testing purposes...

Update: just got Firefox 3 RC1 installed and guess what? Significant again. SunSpider says it's ~1.5 times faster than beta 5, ~8 times faster than 2.0.11 and 10 times faster than IE7(anybody still uses that crap?).
o_O
woot.
and Adblock plugin was ported - no way back for me.

Easy input hints

2007-08-14T08:35:00.000+02:00

Nothing really complex, just trying not to forget how i did that:


<input note="hello world" value="" type="text"/>

and few more lines in javascript:


function updateForms() {
  jQuery(function($) {
    $("form").submit(function() {
      $("input:password", this).each( function() {
        this.value = SHA256(this.value);
      });
    });
    
    $("input:text[@note],textarea[@note]").each(function(){
      if(!this.value && $(this).attr("note")) {
        this.value       = $(this).attr("note");
        this.style.color = "gray";
      }
    })
    .blur(function(){
      if(!this.value && $(this).attr("note")) {
        this.value       = $(this).attr("note");
        this.style.color = "gray";
      }
    })
    .focus(function(){
      if(this.value == $(this).attr("note") && this.style.color == "gray") {
        this.value       = "";
        this.style.color = "black";
      }
    });
    
    $("input:password[@note]").each(function(){
      if(!this.value && $(this).attr("note")) {
        $(this).attr("type", "text");
        this.value       = $(this).attr("note");
        this.style.color = "gray";
      }
    })
    .blur(function(){
      if(!this.value && $(this).attr("note")) {
        $(this).attr("type", "text");
        this.value       = $(this).attr("note");
        this.style.color = "gray";
      }
    })
    .focus(function(){
      if(this.value == $(this).attr("note") && this.style.color == "gray") {
        this.value       = "";
        this.style.color = "black";
        $(this).attr("type", "password");
      }
    });
  });
}

and each time you get new form with AJAX response call updateForms()

Update: added password fields support, function will also affect only fields where note attribute is not empty

ImageScience and RubyInline story

2007-08-01T08:36:00.000+02:00

Just few tips for using installing ImageScience

They say FreeImage and RubyInline is required - yes it's true. In ImageScience docs you can see few-lines-install-guide for FreeImage but don't believe them because you can get huge headake. Do not use CVS! Please! There is an official source distribution and i strongly suggest you to use it. Besides that everything is correct:


make
make install

and you're done.

Second issue i got is RubyInline installation. It goes great after typing


gem install image_science

but loading image_science just silently fails. Reason is rw-rw-rw on .ruby_inline directory in your user profile. Remove "w" from group and others - this should fix it.