First request to Rails app is very slow

Question

always the first request (of a working session) to my Rails app is lagging. Switching to production mode doesn't help.

I use mongrel and the other requests are handled with acceptable speed.

How do I make it faster?

Regards

Answer 1

If you post the contents of the log as that first request is processed then perhaps we can figure out what's making it so slow. For example, this is my log as the first user accesses the site

Booting Mongrel (use 'script/server webrick' to force WEBrick)    
Rails 2.1.0 application starting on http://0.0.0.0:3000    
Debugger enabled    
Call with -d to detach    
Ctrl-C to shutdown server
** Starting Mongrel listening at 0.0.0.0:3000
** Starting Rails with development environment...
/usr/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/mime_type.rb:66: warning: already initialized constant CSV
** Rails loaded.
** Loading any Rails specific GemPlugins
** Signals ready.  TERM => stop.  USR2 => restart.  INT => stop (no restart).
** Rails signals registered.  HUP => reload (without restart).  It might not work well.
** Mongrel 1.1.5 available at 0.0.0.0:3000
** Use CTRL-C to stop.


Processing SessionsController#new (for 127.0.0.1 at 2009-05-26 12:26:00) [GET]
  Session ID: de2acf074759026e1ed6205724f547a9
  Parameters: {"action"=>"new", "controller"=>"sessions"}
Rendering sessions/new
Completed in 0.00587 (170 reqs/sec) | Rendering: 0.00298 (50%) | DB: 0.00092 (15%) | 200 OK [http://localhost/]

I think 170 reqs/sec is fine for our app but others may find that slow. You can see from the stats that rails provides that half of the time required is spent rendering the response - in this case generating the HTML for the login screen. If this request was taking a long time, my first port of call would be the views and helpers associated with the login screen.

If you do have a system that takes a long time to initialize itself on the very first request then why not be sneaky and write your own startup program which first runs rails and then sends a fake request in via curl. That way your users never see the problem.

Chris

Answer 2

It can be because you are:

• requiring and loading a number of plugins and gems

• making a connection to an external service (then caching)

• caching your own pages and that only occurs after the first request unless you 'warm' the cache

Any one of these will inevitably increase the response time of the first request.