Revert "Just add connection management middleware if running in a concurrent environment."

This reverts commit 6b29dc876f.

activerecord/lib/active_record/railtie.rb

@@ -16,7 +16,11 @@ module ActiveRecord
     config.generators.orm :active_record, :migration => true,
                                           :timestamps => true
 
-    config.app_middleware.insert_after "::ActionDispatch::Callbacks", "ActiveRecord::QueryCache"
+    config.app_middleware.insert_after "::ActionDispatch::Callbacks",
+      "ActiveRecord::QueryCache"
+
+    config.app_middleware.insert_after "::ActionDispatch::Callbacks",
+      "ActiveRecord::ConnectionAdapters::ConnectionManagement"
 
     rake_tasks do
       load "active_record/railties/databases.rake"
@@ -74,13 +78,6 @@ module ActiveRecord
       end
     end
 
-    initializer "active_record.add_concurrency_middleware" do |app|
-      if app.config.allow_concurrency
-        app.config.middleware.insert_after "::ActionDispatch::Callbacks",
-          "ActiveRecord::ConnectionAdapters::ConnectionManagement"
-      end
-    end
-
     config.after_initialize do
       ActiveSupport.on_load(:active_record) do
         instantiate_observers

railties/test/application/initializers/frameworks_test.rb

@@ -98,17 +98,7 @@ module ApplicationTests
 
       require "#{app_path}/config/environment"
 
-      expects = [ActiveRecord::QueryCache, ActiveRecord::SessionStore]
-      middleware = Rails.application.config.middleware.map { |m| m.klass }
-      assert_equal expects, middleware & expects
-    end
-
-    test "database middleware initializes when allow concurrency is true" do
-      add_to_config "config.threadsafe!"
-
-      require "#{app_path}/config/environment"
-
-      expects = [ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache]
+      expects = [ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActiveRecord::SessionStore]
       middleware = Rails.application.config.middleware.map { |m| m.klass }
       assert_equal expects, middleware & expects
     end

railties/test/application/middleware_test.rb

@@ -28,6 +28,7 @@ module ApplicationTests
         "ActionDispatch::RemoteIp",
         "Rack::Sendfile",
         "ActionDispatch::Callbacks",
+        "ActiveRecord::ConnectionAdapters::ConnectionManagement",
         "ActiveRecord::QueryCache",
         "ActionDispatch::Cookies",
         "ActionDispatch::Session::CookieStore",