Nginx-Fu: X-Accel-Redirect From Remote Servers
24 Jul2010

We use nginx and its features a lot in Scribd. Many times in the last year we needed some pretty interesting, but not supported feature – we wanted nginx X-Accel-Redirect functionality to work with remote URLs. Out of the box nginx supports this functionality for local URIs only. In this short post I want to explain how did we make nginx serve remote content via X-Accel-Redirect.

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Cool Web Designer is Looking for Work
18 Jul2010

My wife – a good web designer with 6 years of experience with web design, HTML and CSS is looking for a job. Here is some information about her:

We’re physically located in Toronto, Canada, but she has a great experience of working remotely too. So, if you need a web designer or a junior web designer, feel free to contact Tanya.


Advanced Squid Caching in Scribd: Cache Invalidation Techniques
29 May2010

Having a reverse-proxy web cache as one of the major infrastructure elements brings many benefits for large web applications: it reduces your application servers load, reduces average response times on your site, etc. But there is one problem every developer experiences when works with such a cache – cached content invalidation.

It is a complex problem that usually consists of two smaller ones: individual cache elements invalidation (you need to keep an eye on your data changes and invalidate cached pages when related data changes) and full cache purges (sometimes your site layout or page templates change and you need to purge all the cached pages to make sure users will get new visual elements of layout changes). In this post I’d like to look at a few techniques we use at Scribd to solve cache invalidation problems.

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DbCharmer – Rails Can Scale!
16 Apr2010

Back in November 2009 I was working on a project to port Scribd.com code base to Rails 2.2 and noticed that some old plugins we were using in 2.1 were abandoned by their authors. Some of them were just removed from the code base, but one needed a replacement – that was an old plugin called acts_as_readonlyable that helped us to distribute our queries among a cluster of MySQL slaves. There were some alternatives but we didn’t like them for one or another reasons so we’ve decided to go with creating our own ActiveRecord plugin, that would help us scale our databases out. That’s the story behind the first release of DbCharmer.

Today, six months after the first release of the gem and we’ve moved it to gemcutter (which is now the official gems hosting) and we’re already at version 1.6.11. The gem was downloaded more than 2000 times. There are (at least) 10+ large users that rely on this gem to scale their products out. And (this is the most exciting) we’ve added tons of new features to the product.

Here are the main features added since the first release:

  • Much better multi-database migrations support including default migrations connection changing.
  • We’ve added ActiveRecord associations preload support that makes it possible to move eager loading queries to the same connection where your finder queries go to.
  • We’ve improved ActiveRecord’s query logging feature and now you can see what connections your queries executed on (and yes, all those improvements are colorized :-)).
  • We’ve added an ability to temporary remap any ActiveRecord connections to any other connections for a block of code (really useful when you need to make sure all your queries would go to some non-default slave and you do not want to mess with all your models).
  • The most interesting change: we’ve implemented some basic sharding functionality in ActiveRecord which currently is being used in production in our application.

As you can see now DbCharmer helps you to do three major scalability tasks in your Rails projects:

  1. Master-Slave clusters to scale out your Rails models reads.
  2. Vertical sharding by moving some of your models to a separate (maybe even dedicated) servers and still keep using AR associations
  3. Horizontal sharding by slicing your models data to pieces and placing those pieces into different databases and/or servers.

So, If you didn’t check DbCharmer out yet and you’re working on some large rails project that is (or going to be) facing scalability problems, go read the docs, download/install the gem and prove them that Rails CAN scale!


Installing Midnight Commander 4.7 on Mac OS X
2 Feb2010

Another short post just to remember the procedure for the next time I’ll be setting up a new mac. For those of my readers who do not know what Midnight Commander (aka mc) is, GNU Midnight Commander is a visual file manager, created under a heavy influence of Norton Commander file manager from dark DOS ages 🙂 For more information, you can visit their web site. Now, get to the installation topic itself.

To install mc on a Mac OS X machine, you need macports installed and then first thing you’ll need to do is to install some prerequisite libraries:

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$ sudo port install libiconv slang2

Next thing, download the sources from their web site and unpack them. When the sources are ready, you can configure the build:

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$ ./configure \
        --prefix=/opt/mc \
        --with-screen=slang \
        --enable-extcharset \
        --enable-charset \
        --with-libiconv-prefix=/opt/local \
        --with-slang-includes=/opt/local/include \
        --with-slang-libs=/opt/local/lib

Then, normal GNU-style build and install procedure:

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$ make
........
$ sudo make install

And the last thing would be to add /opt/mc/bin to your PATH environment variable.