Rails - how to run method only first time, when user come to my page

Question

I have lots of data in database and I wanna make a statistics from them. Lots of data = thousands rows in table, and I wanna get the daily, weekly, monthly (for every month) stats... just detailed statistics.

The problem is, that the getting these data takes a time (and not little).

So, I think what would be the fastest, clearest and just most effective way to get it...

My first idea - when the user come to my app, in the ApplicationController method I'll fetch from DB stats, save the objects I got into the session's variable and then I will use these variables as a source. Then when I would need somewhere in the app print out the stats, I just use this loaded data.

The question is: is this a good idea? Or, exist any better way?

Answer 1

Instead of storing DB stats in session variable. You can store in memcached

Rails has excellent built-in support for caching

http://memcached.org/

https://github.com/mperham/dalli

Answer 2

Another approach. You can cache parts of pages in per-user basis this way:

- cache [@user, :stat] do # or [@user, :stat, :daily] 
  statistic for the user @user

If some user's associated records affect his statistic then use:

# SomeModel.rb
belongs_to :user, touch: true

This way your user's updated_at will be updated when related model's objects are changed and user's cache will be automatically treated as outdated and block inside - cache ... do will be executed. Make sure that no (or minimum) db hits occur outside this block (e.g.: do not use Model1.where(conditions).all in your controller -- this way you will be making no db-requests, just constructing them).

To enable caching in development mode go to your config/environments/development.rb and change to true parameter config.action_controller.perform_caching and restart your app.