Homo-Adminus Blog

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

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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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.

So, long story short, after a lots of docs and source code reading we’ve found really interesting thing. There is a “feature” added in the recent ActiveMQ release (5.X) called “flow control“, which is used by ActiveMQ core to slow down too fast producers when consumers lag or just aren’t as fast as ActiveMQ wants them to be. This results in unpredictable producers stalls and all kinds of weird problems.

If you’re experiencing the same problems, you could try to add the following to your activemq.xml file to make it stop using flow control and let your producers spool data to the queue as fast as it is possible (that’s exactly what I’d expect from a queue server):

When this is added, all your queues (if they take more than 64Mb of RAM) will start persisting their messages to the disk and freeing your RAM to consume more messages w/o any slowdowns.

Another useful feature we use in our producer is Async Sends which basically means that your producers won’t require any acknowledgments from ActiveMQ after it pushes your messages to a queue. This makes push() operations MUCH faster and your producers’ throughput will become tremendously higher. If you use Java as your producer language, you could use the following code to make your connection async:

After we’ve made the changes explained above, our queue server and producers became rock stable and blazing fast so there is no point to look for another solution because looks like I was right - ActiveMQ is an amazing piece of software - you just need to learn it before using.

This is it for today, if you have any questions, feel free to ask them in the comments and I’d be glad to answer.

Month ago I was on a vacation and as usual even though our hotel provided us with an internet connection on a pretty decent speeds, I wasn’t able to work there because they’ve banned all tcp ports but some major ones (like 80, 21, etc) and I needed to be able to use ssh, mysql, IMs and other non-web software.

After a short research I’ve found a pretty simple to set up and easy to use approach to such a connection problems I’d like to describe here.

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Many people know me as a nginx web server evangelist. But as (IMHO) any professional I think that it is really rewarding to know as much as possible about all the tools available on the market so every time you need to make a decision on some technical issue, you’d consider all pros and cons based on my own knowledge.

This is why when I received an email from Packt company asking if I’d like to read and review their book on Lighttpd I decided to give it a shot (I usually do not review any books because I do not always have enough time to read a book thoroughly to be able to write a review). So, here are my impressions from this book.

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Few months ago I’ve switched one of our internal projects from doing synchronous database saves of analytics data to an asynchronous processing using starling + a pool of workers. This was the day when I really understood the power of specialized queue servers. I was using database (mostly, MySQL) for this kind of tasks for years and sometimes (especially under a highly concurrent load) it worked not so fast… Few times I worked with some queue servers, but those were either some small tasks or I didn’t have a time to really get the idea, that specialized queue servers were created just to do these tasks quickly and efficiently.

All this time (few months now) I was using starling noticed really bad thing in how it works: if workers die (really die, or lock on something for a long time, or just start lagging) and queue start growing, the thing could kill your server and you won’t be able to do something about it - it just eats all your memory and this is it. Since then I’ve started looking for a better solution for our queuing, the technology was too cool to give up. I’ve tried 5 or 6 different popular solutions and all of them sucked… They ALL had the same problem - if your queue grows, this is your problem and not queue broker’s :-/ The last solution I’ve tested was ActiveMQ and either I wasn’t able to push it to its limits or it is really so cool, but looks like it does not have this memory problem. So, we’ve started using it recently.

In this small post I’d like to describe a few things that took me pretty long to figure out in ruby Stomp client: how to make queues persistent (really!) and how to process elements one by one with clients’ acknowledgments.
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Sorry for a short outage today - we were moving to a new server we had some problems because of software incompatibilities on the new box. Now all sites on this box should behave as usual

Since the day one when I joined Scribd, I was thinking about the fact that 90+% of our traffic is going to the document view pages, which is a single action in our documents controller. I was wondering how could we improve this action responsiveness and make our users happier.

Few times I was creating a git branches and hacking this action trying to implement some sort of page-level caching to make things faster. But all the time results weren’t as good as I’d like them to be. So, branches were sitting there and waiting for a better idea.
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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.

Today I was doing some work on one of our database servers (each of them has 4 SAS disks in RAID10 on an Adaptec controller) and it required huge multi-thread I/O-bound read load. Basically it was a set of parallel full-scan reads from a 300Gb compressed innodb table (yes, we use innodb plugin). Looking at the iostat I saw pretty expected results: 90-100% disk utilization and lots of read operations per second. Then I decided to play around with linux I/O schedulers and try to increase disk subsystem throughput. Here are the results:

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