Ruby on Rails

On Sun, Dec 26, 2010 at 11:44 PM, Fearless Fool <lists@ruby-forum.com> wrote:

> What happens in a Rails app between http requests?  Is it torn down
> entirely and re-started at the next request?  I know that's a rather
> open-ended question, but the answer has implications for code such as:
> =====
> class User < ActiveRecord::Base
>  SOME_CONSTANT = difficult_to_compute_initialization_value()
>  ...
> end

By default, in development mode the User class will get redefined in
each request (specifically, in every request that uses it). So the
costly init will be run per request, the benefit is live updates of
new code without server restarts, which is handy for development.

In production mode by default you get the class defined once per
process, so that costly initialization will occur once per process. A
process will typically serve lots of requests, and the process pool is
managed by the software that runs your application, eg Phusion
Passenger.

The flag that controls this behaviour is cache_classes, you'll see it
in config/environments/*.rb.

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