Re: leakage of sockets or activerecord connections

[Eric Wong <normalperson-rMlxZR9MS24@public.gmane.org>]

Corin Langosch <info-FIgL9nsKG9THeUWFKdsAYQC/G2K4zDHf@public.gmane.org> wrote:
> I'm using rainbows to power my own small middleware. I doen't use
> rails (or any other framework), only activerecord for database
> access. I chose XEpollThreadSpawn, set worker_processes 1 and
> worker_connections 25. All classes are eager loaded, no reloading of
> anything while the server is running. AR connection pool size is set
> to 100.

I'm not sure how AR connection pool works (if it uses thread-local
variables for storing the connections).  If it's using thread-locals,
it could be reliant on GC, and that would require:

a) GC to run frequently enough to reap connections
b) your Postgres bindings being GC-aware (and really being unreachable
   in your VM)

> Now it seems that every request opens a new connection and never
> frees/ closes it. So after 100 requests I get an AR connection pool
> exception. I also see exactly 100 postgresql clients connected. When
> I kill the server all clients get disconnected.
> 
> I wonder if I have to setup and hooks (like in unicorn before_fork
> etc.)? In fact I'd expect this happens automatically as the thread
> exits after the request is completed?

Can you reproduce the issue with XEpollThreadPool?

If it's using thread-local storage, you probably need to have a Rack
middleware push the connection back into the pool when it's done working
on a request.

Something like this in your config.ru:

class ReleaseConnections
  def initialize(app)
    @app = app
  end

  def call(env)
    begin
      @app.call(env)
    ensure
      Thread.current[:whatever_sockets].release_to_pool
    end
  end
end

use ReleaseConnections
...
run YourApp.new

In any case, I'd dig through the Rails/AR APIs to see how it works
and how to release resources back to the pool.
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