How to find current connection pool size on heroku

Question

We have a rails 3.2(.11) app with many dynos running on the heroku bamboo stack, connecting to a MySQL RDS server. There seem to be some issues with our current database connect

Answer 1

To check the pool size, start a heroku console heroku run rails c, and run:

ActiveRecord::Base.connection_pool.size

Some webservers such as Puma are multithreaded, so the DB pool size matters. You can also run a multi-threaded worker such as Sidekiq, which also will be affected by the pool size.

Note that Heroku will ignore your database.yml file. To set the pool size you can append ?pool=25 to the DATABASE_URL in your heroku app's configuation.

Answer 2

This information is available via an interface in Rails https://github.com/rails/rails/blob/master/activerecord/lib/active_record/connection_handling.rb#L98-L106 it is in Rails 3+

ActiveRecord::Base.connection_config
# => {:adapter=>"postgresql", :encoding=>"utf8", :pool=>5, :host=>"localhost", :database=>"triage_development"}

You can use this to get the current pool size without needing to eval or relying on the existence of an unexposed instance variable however in rails 3 it may return nil if it hasn't been explicitly set

ActiveRecord::Base.connection_config[:pool]
# => 5