Add puma preloading, decrease DB pool size to size of threads per worker

config/database.yml

 default: &default
   adapter: postgresql
-  pool: 17
+  pool: <%= ENV["DB_POOL"] || ENV['RAILS_MAX_THREADS'] || 5 %>
   timeout: 5000
   encoding: unicode
 

config/puma.rb

@@ -30,7 +30,7 @@ workers ENV.fetch("WEB_CONCURRENCY") { 2 }
 # you need to make sure to reconnect any threads in the `on_worker_boot`
 # block.
 #
-# preload_app!
+preload_app!
 
 # The code in the `on_worker_boot` will be called if you are using
 # clustered mode by specifying a number of `workers`. After each worker
@@ -39,9 +39,9 @@ workers ENV.fetch("WEB_CONCURRENCY") { 2 }
 # or connections that may have been created at application boot, Ruby
 # cannot share connections between processes.
 #
-# on_worker_boot do
-#   ActiveRecord::Base.establish_connection if defined?(ActiveRecord)
-# end
+on_worker_boot do
+  ActiveRecord::Base.establish_connection if defined?(ActiveRecord)
+end
 
 # Allow puma to be restarted by `rails restart` command.
 plugin :tmp_restart