Clearing Out Old Sessions

I got into the habit a while ago of setting up my websites to use ActiveRecord as a session store, this means that the session information for all the visitors to my website is placed in a table in my database. This may or may not be the best way to store sessions but it’s certainly faster than the filesystem and my VPS doesn’t really have the memory capacity for an ‘in memory’ store.

Anyway, one day I decided to perform some DB maintenance, check tables where okay etc, upon logging into the DB however I noticed that my sessions table had grown quite large as was coming up to 125,000 records, little did I realize that the sessions are persisted forever in the DB.

I didn’t think it was the best idea to keep all the session data so wrote the following script and put it in ‘lib/tasks/session.rake’;

namespace :session do
    desc "Prune old session data"
    task :prune => :environment do
        sql = ActiveRecord::Base.connection()
        sql.execute "SET autocommit=0"
        sql.begin_db_transaction
            response = sql.execute("DELETE FROM sessions WHERE `updated_at` < DATE_SUB(CURDATE(), INTERVAL 1 DAY)");
        sql.commit_db_transaction
    end
end

This gave me a ‘session:prune’ rake task. The task removes all sessions older than 1 day from the sessions table. I then added a CRON job for in the following format;

0 0 * * * cd /home/user/railsapp && rake RAILS_ENV=production session:prune > /dev/null 2>&1

The job above basically calls the ‘session:prune’ rake task at midnight every night.

The code in the task in MySQL specific but without a model representing the session table I couldn’t (or at least couldn’t think of a way) to make the code any more ruby-fied. In the event that you do have, or decide to create a session model the following code may work in your task (warning: untested);

Session.destroy_all("created_at" < (Time.now - 1.day))

Hope the above snippet solves at least one of your ActiveRecord session woes.

Check back soon.

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Clearing Out The rFlickr Cache

Assuming you’ve followed the Caching Your Photographs tutorial at some point, you’ll probably have had a lot of fun either deleting the cache every time you upload a new photo or you’ve written your own automated method by now. For those of you that haven’t written your own method of dumping the cache yet, here’s how I do it.

First of all, I created a ‘lib/actions’ folder in the root of my rails project. Inside this folder I created the file ‘photography_action.rb’ with the following contents;

class PhotographyAction
    def self.clear_cache
        ActionController::Base.new.expire_fragment(%r{photography.cache})
    end
end

The above fragment naming assumes that your photos are on a page called ‘photography’ if they are elsewhere, change the fragment to expire that page instead.

Fairly simple I think you’ll agree, you may also be asking yourself ‘why the extra file?’, the main reason for the new file is so that the cache clearing can be executed from a new rake task that doesn’t remove all your cached pages or from an admin page on the website.

You’ll also need to update your ‘config.load_paths’ in ‘environment.rb’. After updating, mine looks like this;

config.load_paths += %W( #{RAILS_ROOT}/app/sweepers #{RAILS_ROOT}/lib/actions )

Inside some action in some, preferably protected, controller somewhere, add the following (redirecting to anywhere you fancy);

PhotographyAction.clear_cache
redirect_to :action => 'index'

Now for the rake task. Inside the directory ‘lib/tasks’ (create it if it doesn’t exists) create the file ‘photography.rake’ then put the following code inside the file;

namespace :photo do
    namespace :cache do
        desc "Clear out photography cache"
        task :clear => :environment do
            PhotographyAction.clear_cache
        end
    end
end

You should then be able to run;

rake photo:cache:clear

From the base of your project in order to clear the cache.

Bear in mind, the code above is literally just a convenient way of clearing out the fragment cache so new photos show up on your photo page, it does not delete photos, nor does it perform a refresh automatically, although, you could add it to a CRON job.

When I get chance, I intend to automate this process and build it into rFlickr along with a new, improved, caching mechanism. I’m sure the above will tide you over for now though.

Check back soon.

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New rFlickr Ruby Gem

After I started to use the rFlickr gem it didn’t take me long to realize that development of the gem had all but halted, yes it worked, which was more than the original Flickr gem did, but it was still a little bit out of date and in the end, a little bit broken.

In one of my older posts I documented a fix for the gem and provided a download to unzip into your plugins folder, however, with the advent of the wonderful GitHub and it’s marvelous gem support I’ve decided to move the project onto GitHub.

I have preserved the original gem’s GPL license and copied the source code from it’s original repository on RubyForge to a new, public, GitHub repository. In the process of the move I have dropped old code from the project, updated the readme & license information and generally performed a little house-keeping.

You can find the project at: http://github.com/digitalpardoe/rflickr/. You can install the gem using one of the following methods. First involves adding GitHub as a gem source (always a good idea) and installing the gem:

$ gem sources -a http://gems.github.com
$ sudo gem install digitalpardoe-rflickr

The second method it to add the gem as a gem dependency to the environment.rb of your Rails project:

config.gem 'digitalpardoe-rflickr', :lib => 'flickr', :source => 'http://gems.github.com'

And run a rake task to install the gem:

$ sudo rake gems:install

Whilst performing the code migration I also added the fix that was documented in my original post and implemented support for the (not so) new ‘farm’ based Flickr URLs for images (which should make things easier to implement).

The future plans for rFlickr include new tests, improved usage examples, updated readme / documentation and implementation of missing API methods, time permitting of course.

Until the readme is updated please refer to the original post for information on how to use rFlickr.

That’s all for now, enjoy the new gem and as they say, if you don’t like it, fork it.

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Guess Who’s Back

As you may have noticed, it’s been a long time since my last post. There isn’t really any good reason for this. Plenty has happened, I just haven’t got round to writing any of it down.

First off I’d like to mention the website, it went through a fairly radical redesign a few months ago and I mentioned nothing about it. For some reason it’s not in my nature to be happy with what I make hence the many faces and iterations of the website. This website, whilst being my home on the internet, is also the test bed for my RoR programming, you may get tired of hearing about it’s re-designs and re-codes but that’s part of the reason I created it. Anyway, another re-design is coming, this time it’s not visual but all back end, the main difference you will notice is that I am doing away with user accounts and having a more open comment system (I could be shooting myself in the foot with this decision, we’ll have to see how the spam bots take it). To the people that have commented on the blog already, your comments will be preserved and, when I roll out the changes, I intend to reply to all the comments I haven’t yet replied to.

The second thing I wanted to mention, again website related, is my hosting. A good proportion of my posts seem to be apologizing for the downtime of the website. I was actually getting pretty bored of this so decided to, quite literally, take matters into my own hands. The website is now hosted on a virtual private server set up and maintained by me. This again, may be a case where I’ve shot myself in the foot. For those of you interested, the VPS is provided by the wonderful folks at Bytemark Hosting.

Number three. Many of the posts of my website relate to the use of the ‘rflickr’ RubyGem. Development of this gem seems to have been at a stand still for a good while now, I’ve therefore taken the decision to clone it and try to continue development in my spare time. More on this in a later post.

Four. Any of you interested in my photography will have noticed a lack of it over the past few months, it’s not that I haven’t been taking any photographs, it’s just that I’ve not published any. To try and remedy this I uploaded a batch of photos today that have been sitting on my computer for a while. You can take a look at them on the photo page of the website or on my Flickr page.

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Arghh, Downtime

Apologies to anyone that has visited the website in the last couple of days, it would appear that there has been a fairly large amount of downtime. Everything is back up and operational again. I will be keeping a closer eye on the status of the website from now on to try and prevent this type of situation arising again. Thanks for your understanding.

Check back soon.

Update: It would also appear that the category browsing is currently broken, I am working on a fix and will push it out shortly.

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