UTOSC Recap
By Josh Tolley
May 10, 2012
I spent three days last week attending the Utah Open Source Conference, in company with Josh Ausborne and Jon Jensen. Since End Point is a “distributed company”, I’d never met Josh Ausborne before, and was glad to spend a few days helping and learning from him as we demonstrated the Liquid Galaxy he has already written about.
This time around, the conference schedule struck me as being particularly oriented toward front-end web development. The talks were chosen based on a vote taken on the conference website, so apparently that’s what everyone wanted, but front-end stuff is not generally my cup of tea. That fact notwithstanding, I found plenty to appeal to my particular interests, and a number of talks I didn’t make it to but wished I had.
I delivered two talks during the conference, the first on database constraints, and the second on Google Earth and the Liquid Galaxy as they apply to geospatial visualization (slides here and here, respectively). Though I couldn’t get past the feeling that my constraints talk dragged quite a bit, it was well received. Where possible I kept it as database-agnostic as possible, but no talk on the subject would be complete without mentioning …
community conference database visionport kamelopard kml
Inherit an application by rewriting the test suite
By Brian Buchalter
May 8, 2012
One of my first tasks at End Point was to inherit a production application from the lead developer who was no longer going to be involved. It was a fairly complex domain model and had passed through many developers’ hands on a tight client budget. Adding to the challenge was the absence of any active development; it’s difficult to “own” an application which you’re not able to make changes to or work with users directly. Moreover, we had a short amount of time; the current developer was leaving in just 30 days. I needed to choose an effective strategy to understand and document the system on a budget.
Taking Responsibility
At the time I was reading Robert C. Martin’s The Clean Coder, which makes a case for the importance of taking responsibility as a “Professional Software Developer”. He defines responsibility for code in the broadest of terms.
Drawing from the Hippocratic oath may seem arrogant, but what better source is there? And, indeed, doesn’t it make sense that the first responsibility, and first goal, of an aspiring professional is to use his or her powers for good?
From there he continues to expound in his declarative style about how to do no harm to the function and …
testing
Monitoring many Postgres files at once with tail_n_mail
By Greg Sabino Mullane
May 8, 2012
This post discusses version 1.25.0 of tail_n_mail, which can be downloaded at https://bucardo.org/tail_n_mail/
One of our clients recently had one of their Postgres servers crash. In technical terms, it issued a PANIC because it tried to commit a transaction that had already been committed. We are using tail_n_mail for this client, and while we got notified six ways to Sunday about the server being down (from Nagios, tail_n_mail, and other systems), I was curious as to why the actual PANIC had not gotten picked up by tail_n_mail and mailed out to us.
The tail_n_mail program at its simplest is a Perl script that greps through log files, finds items of interest, and mails them out. It does quite a bit more than that, of course, including normalizing SQL, figuring out which log files to scan, and analyzing the data on the fly. This particular client of ours consolidates all of their logs to some central logging boxes via rsyslog. For the host in question that issued the PANIC, we had two tail_n_mail config files that looked like this:
## Config file for the tail_n_mail program
## This file is automatically updated
## Last updated: Fri Apr 27 18:00:01 2012
MAILSUBJECT: Groucho …monitoring postgres
Problem with Cisco VPN on Ubuntu 12.04
By Szymon Lipiński
May 7, 2012
A couple of days ago I had to change my notebook. I installed Ubuntu 12.04 on the new one, while on the previous one there was Ubuntu 11.10. There were no problems with copying all the files from the old to the new machine, including GPG and SSH keys. Everything went smoothly and I could connect to all the machines I needed.
The only problem was with VPN. While working for one of our clients, I need to connect to their VPN. On the old machine I did that through the Network Manager. Nothing easier, I went to the Network Manager, chose the Export option and saved all the settings to a file. I copied the file to the new computer and loaded it into the Network Manager.
The file loaded correctly. I could switch the VPN on. It said everything works. But in fact it didn’t. The message was “VPN is connected”, I could switch it on and off, but I couldn’t access any of the client’s resources available from my previous notebook.
The first thing I checked was the content of /etc/resolv.conf on both computers. The file without connecting to VPN looked like this on both computers:
$ cat /etc/resolv.conf
# Generated by NetworkManager
nameserver 127.0.0.1
When I connected to the VPN the files on …
virtualization ubuntu networking
End Point at the Utah Open Source Conference
By Josh Ausborne
May 5, 2012
End Point had a table at the Utah Open Source Conference at Utah Valley University this week. We implemented a “mini Liquid Galaxy” system for the event, and it was a big hit. Most of the other sponsors were offering services or recruiting, but End Point offered a physical item which people could touch and engage with. This allowed us to present our product and services to people, as well as make contact with people who may be interested in joining our team.
Numerous people were really excited about the Liquid Galaxy. The most common thing that people did first when they started using it was to look for their own homes, but they quickly moved onto other areas that contained more 3D building content. They asked questions about the practical application of the system, as well how well it would play games. Multiple other people asked about the ability to build video walls with the system. One of the biggest things that people found interesting about the hardware was the 3D mouse from 3Dconnexion. It took some visitors a while to get the hang of it, but others picked it up quickly and found themselves really liking the way it interacts.
The mini LG consisted of a headless head node, …
conference visionport
Instance Variable Collision with ActsAsTaggableOn
By Brian Gadoury
May 3, 2012
As developers, a lot of what we do is essentially problem solving. Sometimes it’s a problem of how to implement a specific feature. Sometimes it’s a problem with a specific feature. Last week, I ran into a case of the latter in some relatively mature code in the Rails app I was working on.
I was getting a sporadic exception while trying to save an instance of my StoredFile model. I encountered the problem while implementing a pretty trivial boolean field in my model, while I was playing around with it in the rails console. This is where it gets a little weird.
The exception message:
#<NoMethodError: undefined method 'uniq' for "":String>
#Backtrace:
... acts-as-taggable-on-2.2.2/lib/acts_as_taggable_on/acts_as_taggable_on/<b>core.rb</b>:264:in 'block in save_tags'
...rest of backtrace...
Note that none of my work was related to my model’s use of acts_as_taggable_on. I looked briefly at line 264 and its cohorts in core.rb, but nothing jumped out as “a giant, obvious bug in acts-as-taggable-on” (which I wouldn’t expect.) Also, the actual error is a bit suspicious. I love duck typing (and ducks) as much as anyone, but it’s pretty rare to see …
ruby rails
Reverting Git Commits
By Szymon Lipiński
May 2, 2012
Git is great, but it’s not always easy to use. For example, reverting a commit is a very nice feature. There are git commands for reverting a commit which has not been pushed to the main repository. However after pushing it, things are not so easy.
While I was working for one of our clients, I made about 20 commits and then I pushed them to the main repository. After that I realised that I was working on a wrong branch. The new branch I should have used wasn’t created yet. I had to revert all my commits, create the new branch, and load all my changes into it.
Creating the branch named NEW_BRANCH is as easy as:
$ git branch NEW_BRANCH
Now the harder part… how to delete the commits pushed to the main repo. After reading through tons of documentation it turned out that it is not possible. You cannot just delete a pushed commit. However you can do something else.
As an example of this, I created a simple file, added a couple of lines there, and made four commits. The git log looks like this:
$ git log
commit dc47a884f7b303fc8b207550104f5a1de192c91c
Author: Szymon Guz
Date: Mon Apr 30 12:14:21 2012 +0200
replaced b with d
commit 68f56d3321324bd14cd1e73d003b1e151c4d43b4 …git
Profile Ruby with ruby-prof and KCachegrind
By Brian Buchalter
May 1, 2012
This week I was asked to isolate some serious performance problems in a Rails application. I went down quite a few paths to determine how to best isolate the issue. In this post I want to document what tools worked most quickly to help find offending code.
Benchmarks
Before any work begins finding how to speed things up, we need to set a performance baseline so we can know if we are improving things, and by how much. This is done with Ruby’s Benchmark class and some of Rail’s Benchmark class.
The Rails guides would have you setup performance tests, but I found this cumbersome on this Rails 2.3.5 application I was dealing with. Initial attempts to set it up were unfruitful, taking time away from the task at hand. In my case, the process of setting up the test environment to reflect the production environment was prohibitively expensive, but if you can automate the benchmarks, do it. If not, use the logs to measure your performance, and keep track in a spreadsheet. Regardless of benchmarking manually or automatically, you’ll want to keep some kind of log of the results keeping notes about what changed in each iteration.
Isolating the Problem
As always, start with your logs. In Rails, …
performance ruby rails