I'm trying to understand something basic about Rails (and Apache). This is a follow-up to Matt Jones' answer in https://groups.google.com/forum/#!topic/rubyonrails-talk/y6ktv7rL6IA
I repeat his answer here > I suspect `User.exists?` is going to be the lightest possible option. > `User.count == 0` will also work, but I know there are some DBs where that > operation can be expensive on large tables. > > This is still going to do a query every time it checks, so if that's too > much load you could cache the result: > > class User < ActiveRecord::Base > def self.any_users? > @any_users ||= exists? > end > end > > Then your role-defaulting code can check `self.class.any_users?`, which > will only run one query (per server) that returns true. > > NOTE NOTE NOTE: the above is not 100% thread-safe. It assumes that there > is exactly one user sending requests trying to be the first. If you're > worried about somebody racing to sign up for that first account, you'll > want to come up with a more secure approach. > > --Matt Jones > In class User < ActiveRecord::Base def self.any_users? @any_users ||= exists? end end So at some point in the code, I call User.any_users; So Ruby says "Ok, @any_users isn't defined so I'm going to call exists?" That makes perfect sense. Let's say I have several people banging on my website. Do each of them get a completely different copy of Rails? How many copies of @any_users are there? Does @any_users get initialized for each user? What data is common for all threads? What's different for all threads? Where can I learn more about this? I've skimmed https://bearmetal.eu/theden/how-do-i-know-whether-my-rails-app-is-thread-safe-or-not/ but it really isn't helping me understand what is and isn't common between each thread/user/session. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/rubyonrails-talk/abe7fdf1-b381-4e3c-aa7b-04733cadd9c8%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
