Write barriers have gotten some discussion in the Linux world recently which is a good thing due to a lack of documentation about what write barriers are and when they should be used. Let's first start with the assumption that a user wants file system integrity over performance. This often means turning off write caching on all disks. The reason is that file systems rely on the disks not reordering write requests in order to maintain the integrity of the file system. Of course, turning off write caching harms write performance substantially so another option was invented: write barriers.

So I had mentioned that I had encountered difficulties with Rails 2.1 partial updates and I was suspicious of it being related to a plugin. Turns out the flextimes plugin was causing partial updates to not work as well as other subtle errors. The plugin was employed simply to enable a 12-hour with am/pm timeselect and selecttime functions. It had worked fine for a long period of time and only really caused problems with partial updates. However, once I started putting more tests into place I found other problems leading me to believe that flextimes probably broke functionality under Rails 2.0, The problem with unmaintained plugins is that they may continue to do their task but create seemingly unrelated problems elsewhere in the code.

I’m already sold on Passenger and talked it up a bit at RailsConf. Still the list of features coming for version 2 are impressive and should win over some holdouts still using mongrel+nginx and similar setups. Passenger 2.0 will have Rack support, reduced memory usage, fair load balancing, upload buffering, as well as performance and stability improvements. Release Candidate 1 is available now for testing and I may test though I may just wait for 2.0 to be released and upgrade my systems then. More information can be found in the Passenger RC1 Annoucement.

My first web application upgraded to Rails 2.1 completely broke due to partial updates. For some reason, which I’m certainly willing to consider is some plugin or custom code, none of my changed objects ever reported that they were changed. And thus everytime an object was saved no new information was actually placed into the database. I’ve fixed the application by disabling partial updates with “ActiveRecord::Base.partial_updates = false” in environment.rb. Maybe in the future I’ll look into this issue further. Or perhaps I’ll wait for someone else to find it, resolve it, and simply copy the fix. It’s not a feature I need though it would be nice to have.

Update: It seems as though the problem was due to the flextimes plugin. I documented my discovery, changes, and lessons learned in Lessons for Rails: Pay attention to plugins and test everything.

I’ve had a lot of problems with my cd/dvd burner ever since I setup my current desktop. A while back I finally isolated the problem to burning in TAO mode instead of DAO/SAO. I’ve found that since upgrading to Kubuntu 8.04 the problem persists. I have not found a way to configure K3b to only use DAO/SAO and for K3b “Auto” mode seems to always mean TAO. So I have to change the mode each time I burn a CD. I’m not sure if this is a hardware or software problem but it is frustrating.