From 0007501669879a8560090897f78cf1d1b69bf30d Mon Sep 17 00:00:00 2001 From: Eugene Kenny Date: Wed, 26 Sep 2018 03:10:51 +0100 Subject: [PATCH] Only define attribute methods from schema cache To define the attribute methods for a model, Active Record needs to know the schema of the underlying table, which is usually achieved by making a request to the database. This is undesirable behaviour while the app is booting, for two reasons: it makes the boot process dependent on the availability of the database, and it means every new process will make one query for each table, which can cause issues for large applications. However, if the application is using the schema cache dump feature, then the schema cache already contains the necessary information, and we can define the attribute methods without causing any extra database queries. --- .../connection_adapters/schema_cache.rb | 5 ++ activerecord/lib/active_record/core.rb | 4 ++ .../lib/active_record/internal_metadata.rb | 4 ++ activerecord/lib/active_record/railtie.rb | 14 +++- .../lib/active_record/schema_migration.rb | 4 ++ .../connection_adapters/schema_cache_test.rb | 16 +++++ .../test/application/configuration_test.rb | 64 ++++++++++++++++++- 7 files changed, 109 insertions(+), 2 deletions(-) diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb index c29cf1f9a1..c10765f42d 100644 --- a/activerecord/lib/active_record/connection_adapters/schema_cache.rb +++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb @@ -77,6 +77,11 @@ def columns_hash(table_name) }] end + # Checks whether the columns hash is already cached for a table. + def columns_hash?(table_name) + @columns_hash.key?(table_name) + end + # Clears out internal caches def clear! @columns.clear diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb index 392602bc0f..85c87227ff 100644 --- a/activerecord/lib/active_record/core.rb +++ b/activerecord/lib/active_record/core.rb @@ -283,6 +283,10 @@ def type_caster # :nodoc: TypeCaster::Map.new(self) end + def _internal? # :nodoc: + false + end + private def cached_find_by_statement(key, &block) diff --git a/activerecord/lib/active_record/internal_metadata.rb b/activerecord/lib/active_record/internal_metadata.rb index 3626a13d7c..88b0c828ae 100644 --- a/activerecord/lib/active_record/internal_metadata.rb +++ b/activerecord/lib/active_record/internal_metadata.rb @@ -8,6 +8,10 @@ module ActiveRecord # as which environment migrations were run in. class InternalMetadata < ActiveRecord::Base # :nodoc: class << self + def _internal? + true + end + def primary_key "key" end diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb index 81ad9ef3a2..74ccb98159 100644 --- a/activerecord/lib/active_record/railtie.rb +++ b/activerecord/lib/active_record/railtie.rb @@ -140,7 +140,19 @@ class Railtie < Rails::Railtie # :nodoc: initializer "active_record.define_attribute_methods" do |app| config.after_initialize do ActiveSupport.on_load(:active_record) do - descendants.each(&:define_attribute_methods) if app.config.eager_load + if app.config.eager_load + descendants.each do |model| + # SchemaMigration and InternalMetadata both override `table_exists?` + # to bypass the schema cache, so skip them to avoid the extra queries. + next if model._internal? + + # If there's no connection yet, or the schema cache doesn't have the columns + # hash for the model cached, `define_attribute_methods` would trigger a query. + next unless model.connected? && model.connection.schema_cache.columns_hash?(model.table_name) + + model.define_attribute_methods + end + end end end end diff --git a/activerecord/lib/active_record/schema_migration.rb b/activerecord/lib/active_record/schema_migration.rb index f2d8b038fa..1fca1a18f6 100644 --- a/activerecord/lib/active_record/schema_migration.rb +++ b/activerecord/lib/active_record/schema_migration.rb @@ -10,6 +10,10 @@ module ActiveRecord # to be executed the next time. class SchemaMigration < ActiveRecord::Base # :nodoc: class << self + def _internal? + true + end + def primary_key "version" end diff --git a/activerecord/test/cases/connection_adapters/schema_cache_test.rb b/activerecord/test/cases/connection_adapters/schema_cache_test.rb index 67496381d1..727cab77f5 100644 --- a/activerecord/test/cases/connection_adapters/schema_cache_test.rb +++ b/activerecord/test/cases/connection_adapters/schema_cache_test.rb @@ -91,6 +91,22 @@ def test_clear_data_source_cache @cache.clear_data_source_cache!("posts") end + test "#columns_hash? is populated by #columns_hash" do + assert_not @cache.columns_hash?("posts") + + @cache.columns_hash("posts") + + assert @cache.columns_hash?("posts") + end + + test "#columns_hash? is not populated by #data_source_exists?" do + assert_not @cache.columns_hash?("posts") + + @cache.data_source_exists?("posts") + + assert_not @cache.columns_hash?("posts") + end + private def schema_dump_path diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb index 9b01d42b1e..2220caf257 100644 --- a/railties/test/application/configuration_test.rb +++ b/railties/test/application/configuration_test.rb @@ -331,7 +331,7 @@ class Post < ActiveRecord::Base assert_not_includes Post.instance_methods, :title end - test "eager loads attribute methods in production" do + test "does not eager load attribute methods in production when the schema cache is empty" do app_file "app/models/post.rb", <<-RUBY class Post < ActiveRecord::Base end @@ -354,9 +354,71 @@ class Post < ActiveRecord::Base app "production" + assert_not_includes Post.instance_methods, :title + end + + test "eager loads attribute methods in production when the schema cache is populated" do + app_file "app/models/post.rb", <<-RUBY + class Post < ActiveRecord::Base + end + RUBY + + app_file "config/initializers/active_record.rb", <<-RUBY + ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:") + ActiveRecord::Migration.verbose = false + ActiveRecord::Schema.define(version: 1) do + create_table :posts do |t| + t.string :title + end + end + RUBY + + add_to_config <<-RUBY + config.eager_load = true + config.cache_classes = true + RUBY + + app_file "config/initializers/schema_cache.rb", <<-RUBY + ActiveRecord::Base.connection.schema_cache.add("posts") + RUBY + + app "production" + assert_includes Post.instance_methods, :title end + test "does not attempt to eager load attribute methods for models that aren't connected" do + app_file "app/models/post.rb", <<-RUBY + class Post < ActiveRecord::Base + end + RUBY + + app_file "config/initializers/active_record.rb", <<-RUBY + ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:") + ActiveRecord::Migration.verbose = false + ActiveRecord::Schema.define(version: 1) do + create_table :posts do |t| + t.string :title + end + end + RUBY + + add_to_config <<-RUBY + config.eager_load = true + config.cache_classes = true + RUBY + + app_file "app/models/comment.rb", <<-RUBY + class Comment < ActiveRecord::Base + establish_connection(adapter: "mysql2", database: "does_not_exist") + end + RUBY + + assert_nothing_raised do + app "production" + end + end + test "initialize an eager loaded, cache classes app" do add_to_config <<-RUBY config.eager_load = true -- GitLab