My app keeps creating database connections, how do I trace the reason?

Question

I have a Ruby on Rails application running on Heroku. I keep getting these messages in the log:

2015-05-05T16:11:14Z app[postgres.27102]: [AQUA] connection received: host=xx.xxx.xx.26 port=60278
2015-05-05T16:11:14Z app[postgres.27102]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:14Z app[postgres.27103]: [AQUA] connection received: host=xx.xxx.xx.26 port=60291
2015-05-05T16:11:14Z app[postgres.27103]: [AQUA] connection authorized: user=postgres database=postgres
2015-05-05T16:11:18Z app[postgres.27104]: [AQUA] connection received: host=xx.xxx.x.166 port=54180
2015-05-05T16:11:18Z app[postgres.27104]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:23Z app[postgres.27105]: [AQUA] connection received: host=xx.xxx.x.166 port=55488
2015-05-05T16:11:23Z app[postgres.27105]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:28Z app[postgres.27106]: [AQUA] connection received: host=xx.xxx.x.166 port=56774
2015-05-05T16:11:28Z app[postgres.27106]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:28Z app[postgres.27107]: [AQUA] connection received: host=xx.xxx.x.166 port=56854
2015-05-05T16:11:28Z app[postgres.27107]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:28Z app[postgres.27108]: [AQUA] connection received: host=xx.xxx.x.166 port=56885
2015-05-05T16:11:28Z app[postgres.27108]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:28Z app[postgres.27109]: [AQUA] connection received: host=xx.xxx.x.166 port=56912
2015-05-05T16:11:28Z app[postgres.27109]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:33Z app[postgres.27110]: [AQUA] connection received: host=xx.xxx.x.166 port=58039
2015-05-05T16:11:33Z app[postgres.27110]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:38Z app[postgres.27111]: [AQUA] connection received: host=xx.xxx.x.166 port=59387
2015-05-05T16:11:38Z app[postgres.27111]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:43Z app[postgres.27112]: [AQUA] connection received: host=xx.xxx.x.166 port=60944
2015-05-05T16:11:43Z app[postgres.27112]: [AQUA] connection authorized: user=postgres database=somedb
2015-05-05T16:11:14+00:00 app[heroku-postgres]: source=HEROKU_POSTGRESQL_AQUA sample#current_transaction=511990 sample#db_size=203303096bytes sample#tables=17 sample#active-connections=2 sample#waiting-connections=0 sample#index-cache-hit-rate=0.99997 sample#table-cache-hit-rate=0.94699 sample#load-avg-1m=0.14 sample#load-avg-5m=0.25 sample#load-avg-15m=0.24 sample#read-iops=0.1875 sample#write-iops=1 sample#memory-total=7629448kB sample#memory-free=428388kB sample#memory-cached=6784860kB sample#memory-postgres=171732kB

I can't figure out what's causing this. The application runs Cedar 10 stack, ruby 2.1.4, rails 3.2.11 and puma 2.11.2 with 3 workers and 1 thread. It's not happening in the development or staging environments, only on Heroku.

Running: select application_name from pg_stat_activity; shows:

        application_name         
---------------------------------

 puma: cluster worker 2: 3 [app]
 puma: cluster worker 1: 3 [app]
 puma: cluster worker 0: 3 [app]
 psql johnny interactive

Here's my puma configuration file (min and max threads is equal to 1):

workers Integer(ENV['PUMA_WORKERS'] || 3)
threads Integer(ENV['MIN_THREADS']  || 1), Integer(ENV['MAX_THREADS'] || 16)

preload_app!

rackup      DefaultRackup
port        ENV['PORT']     || 3000
environment ENV['RACK_ENV'] || 'development'

on_worker_boot do
  # worker specific setup
  ActiveSupport.on_load(:active_record) do
    config = ActiveRecord::Base.configurations[Rails.env] ||
                Rails.application.config.database_configuration[Rails.env]
    config['pool'] = ENV['MAX_THREADS'] || 16
    ActiveRecord::Base.establish_connection(config)
  end
end

Any ideas on how to trace this?

Update: I added a debug message to the on_worker_boot block and it only gets invoked on the application startup, so I still have no clue why connections are beings established so frequently.

Answer 1

This is casual logs about establish connection to Postgres. So, just ignore them or try to disable them in postgresql.conf (see log_connections option), but I don't think that you have access to it in Heroku.