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:
- Allows you to easily manage AR models’ connections (
switch_connection_to method)
- Allows you to switch AR models’ default connections to a separate servers/databases
- Allows you to easily choose where your query should go (
on_* methods family)
- Allows you to automatically send read queries to your slaves while masters would handle all the updates.
- Adds multiple databases migrations to ActiveRecord
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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 
Today I’ve managed to finish initial version of our bounces-handler package we use for mailing-related stuff in Scribd.
Bounces-handler package is a simple set of scripts to automatically process email bounces and ISP‘s feedback loops emails, maintain your mailing blacklists and a Rails plugin to use those blacklists in your RoR applications.
This piece of software has been developed as a part of more global work on mailing quality improvement in Scribd.com, but it was one of the most critical steps after setting up reverse DNS records, DKIM and SPF.
The package itself consists of two parts:
- Perl scripts to process incoming email:
- bounces processor — could be assigned to process all your bounce emails
- feedback loops messages processor — more specific for Scribd, but still – could be modified for your needs (will be released soon).
- Rails plugin to work with mailing blacklists
For more information, please check our README file. If you have any questions, comments or suggestions, please leave them here as a comments and I’ll try to reply as soon as possible.
We were using memcache in our application for a long time and it helped a lot to reduce DB servers load on some huge queries. But there was a problem (sometimes called a “dog-pile effect”) – when some cached value was expired and we had a huge traffic, sometimes too many threads in our application were trying to calculate new value to cache it.
For example, if you have some simple but really bad query like
1
| SELECT COUNT(*) FROM some_table WHERE some_flag = X |
which could be really slow on a huge tables, and your cache expires, then ALL your clients calling a page with this counter will end up waiting for this counter to be updated. Sometimes there could be tens or even hundreds of such a queries running on your DB killing your server and breaking an entire application (number of application instances is constant, but more and more instances are locked waiting for a counter).
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How often do we think about our http sessions implementation? I mean, do you know, how your currently used sessions-related code will behave when sessions number in your database will grow up to millions (or, even, hundreds of millions) of records? This is one of the things we do not think about. But if you’ll think about it, you’ll notice, that 99% of your session-related operations are read-only and 99% of your sessions writes are not needed. Almost all your sessions table records have the same information: session_id and serialized empty session in the data field.
Looking at this sessions-related situation we have created really simple (and, at the same time, really useful for large Rails projects) plugin, which replaces ActiveRecord-based session store and makes sessions much more effective. Below you can find some information about implementation details and decisions we’ve made in this plugin, but if you just want to try it, then check out our project site.
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Because of not fully correct testing methodology, benchmark results are not fully correct. So, I decided to redo all tests. New benchmark results you can get in “Looking For Optimal Solution” series Summary post.
This week we have started one new project with Ruby on Rails as primary framework. My first task was to prepare runtime environment for it on one of our development servers. When I have tried to research how people doing it, I noted that there is no information about how to deploy rails application with nginx as frontend and what is performance of such solution. Before blindly make any decisions about future platform I’ve decided to make some performance tests of the some most popular rails web servers/frontends. Results of these tests you can find here with configuration samples for all software that I have used.
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