ActiveRecord::ConnectionTimeoutError on rails model callbacks

[alenteria]

I am using EM.def in some of my rails Model callbacks and sometimes it throws error
ActiveRecord::ConnectionTimeoutError (could not obtain a database connection within 5.000 seconds (waited 5.000 seconds))

[sodabrew]

Please provide enough information for this bug report.

[alenteria]

My model Photo, has an attached file used with paperclip.
Theres a callback 'generate_watermarked_preview' on after_commit
I enclosed the watermark generation logic with Event Machine.
It looks something like this

EM.run do
      non_blocking = proc do
        .. some codes here
      end
     EM.defer non_blocking
end

But if I uploaded many photos and this callback was being called many times, it throws this error
ActiveRecord::ConnectionTimeoutError (could not obtain a database connection within 5.000 seconds (waited 5.000 seconds))

[sodabrew]

Some related discussion: https://www.ruby-forum.com/topic/195010
I think the idea is that you may be creating / checking out new connections from the shared pool faster then you're checking them back in. Which database adapter are you using, btw?

[alenteria]

I am using postgresql.
Ok thanks @sodabrew. I'll read that forum.

[alenteria]

I solved it by making sure the connection pool has been released.
ActiveRecord::Base.connection_pool.release_connection

EM.run do
      non_blocking = proc do
        begin
          .. some codes here
        ensure
           ActiveRecord::Base.connection_pool.release_connection
        end
     end
     EM.defer non_blocking
end

[sodabrew]

Good to hear! Do you think there's some documentation improvements you could suggest to help this situation?

[alenteria]

Yes, much better if you provide more examples in different scenarios.