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

config/database.yml

@@ -1,8 +1,11 @@
 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 } %>
+  # Puma: 3 threads × 1 worker = 3 connections
+  # GoodJob: 5 queue threads + 3 system threads = 8 connections
+  # Buffer: 5 additional connections
+  # Total: 16 connections
+  pool: <%= ENV.fetch("DB_POOL_SIZE") { 16 } %>
   host: <%= ENV.fetch("DB_HOST") { "127.0.0.1" } %>
   port: <%= ENV.fetch("DB_PORT") { "5432" } %>
   user: <%= ENV.fetch("POSTGRES_USER") { nil } %>

spec/models/database_connection_pool_spec.rb

@@ -0,0 +1,48 @@
+require 'rails_helper'
+
+RSpec.describe "Database Connection Pool" do
+  it "has the correct pool size configuration" do
+    expected_pool_size = ENV.fetch("DB_POOL_SIZE") { 16 }.to_i
+    actual_pool_size = ActiveRecord::Base.connection.pool.size
+
+    expect(actual_pool_size).to eq(expected_pool_size)
+  end
+
+  it "handles concurrent database operations without connection timeout" do
+    threads = []
+    mutex = Mutex.new
+    error_occurred = false
+
+    10.times do
+      threads << Thread.new do
+        begin
+          User.transaction do
+            mutex.synchronize do
+              User.count
+              sleep 0.1 # Simulate some work
+            end
+          end
+        rescue ActiveRecord::ConnectionTimeoutError
+          mutex.synchronize { error_occurred = true }
+        end
+      end
+    end
+
+    threads.each(&:join)
+    expect(error_occurred).to be false
+  end
+
+  it "respects custom pool size from environment variable" do
+    original_pool_size = ENV["DB_POOL_SIZE"]
+    ENV["DB_POOL_SIZE"] = "20"
+
+    # Force reconnection to apply new pool size
+    ActiveRecord::Base.establish_connection
+
+    expect(ActiveRecord::Base.connection.pool.size).to eq(20)
+
+    # Cleanup
+    ENV["DB_POOL_SIZE"] = original_pool_size
+    ActiveRecord::Base.establish_connection
+  end
+end