Fix: ActiveRecord::ConnectionTimeoutError (MAYBE-RAILS-CZ)

config/database.yml

@@ -1,8 +1,10 @@
 default: &default
   adapter: postgresql
   encoding: unicode
-  # 3 connections for Puma, 8 for GoodJob (in async mode, the default for self-hosters) = 11 connections
-  pool: <%= ENV.fetch("DB_POOL_SIZE") { 11 } %>
+  pool: <%= ENV.fetch("DB_POOL_SIZE") {
+    (ENV.fetch("WEB_CONCURRENCY") {1}.to_i * ENV.fetch("RAILS_MAX_THREADS") {3}.to_i) +
+    ENV.fetch("GOOD_JOB_MAX_THREADS") {5}.to_i
+  } %>
   host: <%= ENV.fetch("DB_HOST") { "127.0.0.1" } %>
   port: <%= ENV.fetch("DB_PORT") { "5432" } %>
   user: <%= ENV.fetch("POSTGRES_USER") { nil } %>

spec/config/database_yml_spec.rb

@@ -0,0 +1,38 @@
+require 'rails_helper'
+require 'yaml'
+
+RSpec.describe 'database.yml configuration' do
+  let(:config) { YAML.load(ERB.new(File.read('config/database.yml')).result) }
+
+  describe 'connection pool size' do
+    before do
+      ENV['DB_POOL_SIZE'] = nil
+      ENV['WEB_CONCURRENCY'] = nil
+      ENV['RAILS_MAX_THREADS'] = nil
+      ENV['GOOD_JOB_MAX_THREADS'] = nil
+    end
+
+    after do
+      ENV['DB_POOL_SIZE'] = nil
+      ENV['WEB_CONCURRENCY'] = nil
+      ENV['RAILS_MAX_THREADS'] = nil
+      ENV['GOOD_JOB_MAX_THREADS'] = nil
+    end
+
+    it 'calculates default pool size correctly' do
+      expect(config['default']['pool']).to eq(8) # (1 * 3) + 5
+    end
+
+    it 'uses custom pool size when DB_POOL_SIZE is set' do
+      ENV['DB_POOL_SIZE'] = '20'
+      expect(YAML.load(ERB.new(File.read('config/database.yml')).result)['default']['pool']).to eq(20)
+    end
+
+    it 'calculates pool size based on environment variables' do
+      ENV['WEB_CONCURRENCY'] = '2'
+      ENV['RAILS_MAX_THREADS'] = '4'
+      ENV['GOOD_JOB_MAX_THREADS'] = '6'
+      expect(YAML.load(ERB.new(File.read('config/database.yml')).result)['default']['pool']).to eq(14) # (2 * 4) + 6
+    end
+  end
+end