Can't obtain database connection within 5 seconds - Sidekiq workers, Unicorn, Redis ToGo on Heroku - postgresql

Question

I've a bunch background tasks (Sidekiq workers) that update database, and I keep getting this failing thread exception.
Heroku Log: WARN: could not obtain a database connection within 5.000 seconds (waited 5.001 seconds)
Heroku
Heroku Postgres :: Olive - 20 connections limit.
Redis ToGo - 10 connections limit.
Sidekiq - 2 connections.
Each client request create ~50 threads - finally ~20 threads trying to update db.
Now I know this is too much threads trying to make connection (updating Active:Record..).
I don't mind them to wait in try again until success.
-config/unicorn.rb
worker_processes Integer(ENV["WEB_CONCURRENCY"] || 3)
timeout 30
preload_app true
before_fork do |server, worker|
Signal.trap 'TERM' do
puts 'Unicorn master intercepting TERM and sending myself QUIT instead'
Process.kill 'QUIT', Process.pid
end
if defined?(ActiveRecord::Base)
ActiveRecord::Base.connection.disconnect!
end
end
after_fork do |server, worker|
Signal.trap 'TERM' do
puts 'Unicorn worker intercepting TERM and doing nothing. Wait for master to send QUIT'
end
if defined?(ActiveRecord::Base)
config = ActiveRecord::Base.configurations[Rails.env] ||
Rails.application.config.database_configuration[Rails.env]
config['pool'] = ENV['DB_POOL'] || 2
config['reaping_frequency'] = ENV['DB_REAP_FREQ'] || 10 # seconds
ActiveRecord::Base.establish_connection(config)
end
end
-config/initializers/sidekiq.rb
require 'sidekiq'
Sidekiq.configure_server do |config|
if(database_url = ENV['DATABASE_URL'])
p pool_size = Sidekiq.options[:concurrency] + 2
p ENV['DATABASE_URL'] = "#{database_url}?pool=#{pool_size}"
ActiveRecord::Base.establish_connection
end
end
--condig/sidekiq.yml
:concurrency: 2
Thanks a lot for all the help,
Eldar