So, I’ve seeing some quirking behavior with my app after launching it
into my production environment (railsmachine). The weirdness only
(sporadically) occurs when I’m running a mongrel cluster. The app runs
fine (locally and in production) when I run on a single mongrel. I’m
hoping somebody on the forum can help me out, as I’ve run out of things
to try given my limited rails experience 
Environment
My railsmachine environment consists of Apache load-balancing 2 mongrel
instances connecting to a single (non-clustered) MySQL instance. All
these processes run in a single VPS. I set up the VPS per the
RailsMachine “operating manual”:
https://support.railsmachine.com/index.php?pg=kb.book&id=4 . Rails
version is 1.2.3 (I can list my gems if requested, but I don’t think
they’re applicable to the problem)
The Problem
The problem is sporadic and difficult to reproduce, but when it does
occur, it usually looks like this:
- Go to the “edit” page and update an existing record (e.g. set one of
the boolean flags on the record from true to false or vice-versa). The
changes are correctly persisted to the DB via ActiveRecord (I verified
this with mysql client). - Load the “view” page that displays all records: the OLD version of the
record is displayed - Refresh (via the browser’s refresh button) the “view” page: The
changes are now reflected in the view (i.e. the view is in sync with
the DB state) - Refresh the “view” page again: The view toggles back to the OLD
version of the record. - and so on…
Given this behavior, I’m guessing the problem is due to one of the
mongrels caching a stale version of the page (or model?). Perhaps the
mongrel that performed DB update flushed it’s cache while the other
mongrel kept the stale version of the page/model? In this case, the
fact that the view page toggles between stale and fresh on browser would
suggest that the Apache load balancing is performed round-robin.
However, this is just a hypothesis…
Debugging
My application is fairly simple
- 4 database tables
- no session state
- no page or action caching
- simple (hand-coded) caching of static database tables
But, I wanted to boil the problem to something really simple for
debugging purposes. SO, I wrote the following controller:
START games_controller.rb
class GamesController < ApplicationController
session :off
View Games Status Page
def view
user_id = params[:user_id]
# This is an ActiveRecord "dynamic finder"
@participant = Participant.find_by_user_id(user_id)
# a Participant has_many Games. I'm using (true) here to force
# a collection refresh (just to be safe)
@games = @participant.games(true)
end
end
END games_controller.rb
I can reproduce the bug even with this simple controller, leading me to
believe the problem must lie in my environment and not my code. I
verified (via the logs) the controller code is executing on each request
(i.e. rails isn’t caching my action). After some futile
logging/debugging efforts, I then tried turning the following knobs
(testing between each step, of course):
- Turn off rails action caching
- Turn off the MySQL query_cache
- Restart MySQL, Apache. Redeploy mongrels (via capistrano)
However, none of this seemed to help. Here is the production environment
configuration file I ended up with (excluding app-specific ENV entries)
START production.rb
config.cache_classes = true
config.action_controller.consider_all_requests_local = false
config.action_controller.perform_caching = false
END production.rb
So, I’m at a loss at this point. I’m a rails noob (Java’s my main
thing), so I can only assume that I’m doing something stupid on my VPS.
I contacted railsmachine support, and, unfortunately, they were of
little help (“Did you check the logs?”). Any help you could offer would
be greatly appreciated. Solutions, suggestions, anything
Thanks in advance!
-nick