Oleksiy Kovyrin

Yet Another Admin's Blog

DbCharmer – Rails Can Scale!

Posted by Oleksiy Kovyrin under Databases, Development, My Projects

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

Posted by Oleksiy Kovyrin under Admin-tips, General

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.

Enabling IPv6 Support in nginx

Posted by Oleksiy Kovyrin under Admin-tips, Networks

This is going to be a really short post, but for someone it could save an hour of life.

So, you’ve nothing to do and you’ve decided to play around with IPv6 or maybe you’re happened to be an administrator of a web service that needs to support IPv6 connectivity and you need to make your nginx server work nicely with this protocol.

First thing you need to do is to enable IPv6 in nginx by recompiling it with --with-ipv6 configure option and reinstalling it. If you use some pre-built package, check if your nginx already has this key enabled by running nginx -V.

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DB Charmer – ActiveRecord Connection Magic Plugin

Posted by Oleksiy Kovyrin under Databases, Development, My Projects

Today I’m proud to announce the first public release of our ActiveRecord database connection magic plugin: DbCharmer.

DB Charmer – ActiveRecord Connection Magic Plugin

DbCharmer is a simple yet powerful plugin for ActiveRecord that does a few things:

  1. Allows you to easily manage AR models’ connections (switch_connection_to method)
  2. Allows you to switch AR models’ default connections to a separate servers/databases
  3. Allows you to easily choose where your query should go (on_* methods family)
  4. Allows you to automatically send read queries to your slaves while masters would handle all the updates.
  5. Adds multiple databases migrations to ActiveRecord

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Advanced Squid Caching in Scribd: Logged In Users and Complex URLs Handling

Posted by Oleksiy Kovyrin under Admin-tips, Development, My Projects

It’s been a while since I’ve posted my first post about the way we do document pages caching in Scribd and this approach has definitely proven to be really effective since then. In the second post of this series I’d like to explain how we handle our complex document URLs and logged in users in the caching architecture.

First of all, let’s take a look at a typical Scribd’s document URL: http://www.scribd.com/doc/1/Improved-Statistical-Test.

As we can see, it consists of a document-specific part (/doc/1) and a non-unique human-readable slug part (/Improved-Statistical-Test). When a user comes to the site with a wrong slug in the document URL, we need to make sure we send the user to the correct URL with a permanent HTTP 301 redirect. So, obviously we can’t simply send our requests to the squid because it’d cause few problems:

  • When we change document’s title, we’d create a new cached item and would not be able to redirect users from the old URL to the new one
  • When we change a title, we’d pollute cache with additional document page copies.

One more problem that makes the situation even worse – we have 3 different kinds of users on the site:

  1. Logged in users – active web site users that are logged in and should see their name at the top of the page, should see all kinds of customized parts of the page, etc (especially when a page is their own document).
  2. Anonymous users – all users that are not logged in and visit the site with a flash-enabled browser
  3. Bots – all kinds of crawlers that can’t read flash content and need to see a plain text document version

All three kinds of users should see their own document page versions whether the page is cached or not.

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The Blog v.2.0

Posted by Oleksiy Kovyrin under Blog, My Projects

Long time ago, in 2002 I decided to create my own point of presence in the Internet. Back then I’ve got pretty nice domain (scoundrel.kremenchug.net), hacked up a few pages on php, added a guestbook and that was it. Many years it was almost static and I did a few updates on my resume page few times a year. Later I’ve switched the site to wordpress to make it easier to manage my resume and stuff…

And 3 years ago in March 2006 I’ve decided to start my own blog. I took a standard template and started the blog on a separate domain while the domain was on its own domain name… This spring my wife made me a great birthday present – she’s created me a custom blog design that has all the stuff I wanted from my own web site for a long time. My friend Dima Shteflyuk has helped me with creating a wordpress template from Tanya’s mockups and here we are – now I’ve decided to merge my blog and my web site into a single web entity called http://kovyrin.net/. Welcome to my new blog/site/whatever!

Loops plugin for rails and merb released

Posted by Oleksiy Kovyrin under Development, Links, My Projects

loops is a small and lightweight framework for Ruby on Rails and Merb created to support simple background loops in your application which are usually used to do some background data processing on your servers (queue workers, batch tasks processors, etc).

Originally loops plugin was created to make our (Scribd.com) own loops code more organized. We used to have tens of different modules with methods that were called with script/runner and then used with nohup and other not so convenient backgrounding techniques. When you have such a number of loops/workers to run in background it becomes a nightmare to manage them on a regular basis (restarts, code upgrades, status/health checking, etc).

After a short time of writing our loops in more organized ways we were able to generalize most of the loops code so now our loops look like a classes with a single mandatory public method called run. Everything else (spawning many workers, managing them, logging, backgrounding, pid-files management, etc) is handled by the plugin itself.

The major idea behind this small project was to create a deadly simple and yet robust framework to be able to run some tasks in background and do not think about spawning many workers, restarting them when they die, etc. So, if you need to be able to run either one or many copies of your worker or you do not want to think about re-spawning dead workers and do not want to spend megabytes of RAM on separate copies of Ruby interpreter (when you run each copy of your loop as a separate process controlled by monit/god/etc), then I’d recommend you to try this framework — you’ll like it.

For more information, visit the project site and, of course, read the sources :-)

Rails Developer for a Large Startup: My Vision of an Ideal Candidate

Posted by Oleksiy Kovyrin under Databases, Development, General, Links

Few days ago we were chatting in our corporate Campfire room and one of the guys asked me what do I think about Rails developers hiring process, what questions I’d ask a candidate, etc… This question started really long and interesting discussion and I’d like to share my thoughts on this question in this post.

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ActiveMQ Tips: Flow Control and Stalled Producers Problem

Posted by Oleksiy Kovyrin under Admin-tips, Development

It’s been a few months since we‘ve started actively using ActiveMQ queue server in our project. For some time we had pretty weird problems with it and even started thinking about switching to something else or even writing our own queue server which would comply with our requirements. The most annoying problem was the following: some time after activemq restart everything worked really well and then activemq started lagging, queue started growing and all producer processes were stalling on push() operations. We rewrote our producers from Ruby to JRuby, then to Java and still – after some time everything was in a bad shape until we restarted the queue server.

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