implements automatic EXPLAIN logging for slow queries

7 files changed, 38 insertions, 1 deletions

diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index d158fdd46f..a324486d6f 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,6 +1,11 @@
 ## Rails 3.2.0 (unreleased) ##
 
-*   Add DebugExceptions middleware which contains features extracted from ShowExceptions middleware *José Valim*
+*   New applications get a flag
+    `config.active_record.auto_explain_threshold_in_seconds` in the evironments
+    configuration files. With a value of 0.5 in development.rb, and commented
+    out in production.rb. No mention in test.rb. *fxn*
+
+*   Display mounted engine's routes in `rake routes`. *Piotr Sarnacki*
 
 *   Display mounted engine's routes in `rake routes` *Piotr Sarnacki*
 
diff --git a/railties/guides/code/getting_started/config/environments/development.rb b/railties/guides/code/getting_started/config/environments/development.rb
index 89932bf19b..d60a10568b 100644
--- a/railties/guides/code/getting_started/config/environments/development.rb
+++ b/railties/guides/code/getting_started/config/environments/development.rb
@@ -22,6 +22,13 @@ Blog::Application.configure do
   # Only use best-standards-support built into browsers
   config.action_dispatch.best_standards_support = :builtin
 
+  # Raise exception on mass assignment protection for ActiveRecord models
+  config.active_record.mass_assignment_sanitizer = :strict
+
+  # Log the query plan for queries taking more than this (works
+  # with SQLite, MySQL, and PostgreSQL)
+  config.active_record.auto_explain_threshold_in_seconds = 0.5
+
   # Do not compress assets
   config.assets.compress = false
 
diff --git a/railties/guides/code/getting_started/config/environments/production.rb b/railties/guides/code/getting_started/config/environments/production.rb
index dee8acfdfe..c9b2f41c39 100644
--- a/railties/guides/code/getting_started/config/environments/production.rb
+++ b/railties/guides/code/getting_started/config/environments/production.rb
@@ -60,4 +60,8 @@ Blog::Application.configure do
 
   # Send deprecation notices to registered listeners
   config.active_support.deprecation = :notify
+
+  # Log the query plan for queries taking more than this (works
+  # with SQLite, MySQL, and PostgreSQL)
+  # config.active_record.auto_explain_threshold_in_seconds = 0.5
 end
diff --git a/railties/guides/source/configuring.textile b/railties/guides/source/configuring.textile
index d91011c370..24bf9d863b 100644
--- a/railties/guides/source/configuring.textile
+++ b/railties/guides/source/configuring.textile
@@ -268,6 +268,8 @@ h4. Configuring Active Record
 
 * +config.active_record.identity_map+ controls whether the identity map is enabled, and is false by default.
 
+* +config.active_record.auto_explain_threshold_in_seconds+ configures the threshold for automatic EXPLAINs (+nil+ disables this feature). Queries taking more than those many seconds get their query plan logged. Default is 0.5 in development mode.
+
 The MySQL adapter adds one additional configuration option:
 
 * +ActiveRecord::ConnectionAdapters::MysqlAdapter.emulate_booleans+ controls whether Active Record will consider all +tinyint(1)+ columns in a MySQL database to be booleans and is true by default.
diff --git a/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt
index 47078e3af9..beaf941282 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt
@@ -25,6 +25,10 @@
   <%- unless options.skip_active_record? -%>
   # Raise exception on mass assignment protection for ActiveRecord models
   config.active_record.mass_assignment_sanitizer = :strict
+
+  # Log the query plan for queries taking more than this (works
+  # with SQLite, MySQL, and PostgreSQL)
+  config.active_record.auto_explain_threshold_in_seconds = 0.5
   <%- end -%>
 
   # Do not compress assets
diff --git a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
index 50f2df3d35..40ec3fc644 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/environments/production.rb.tt
@@ -60,4 +60,10 @@
 
   # Send deprecation notices to registered listeners
   config.active_support.deprecation = :notify
+
+  <%- unless options.skip_active_record? -%>
+  # Log the query plan for queries taking more than this (works
+  # with SQLite, MySQL, and PostgreSQL)
+  # config.active_record.auto_explain_threshold_in_seconds = 0.5
+  <%- end -%>
 end
diff --git a/railties/test/generators/app_generator_test.rb b/railties/test/generators/app_generator_test.rb
index 235c08e38e..41bb4d8b20 100644
--- a/railties/test/generators/app_generator_test.rb
+++ b/railties/test/generators/app_generator_test.rb
@@ -336,6 +336,15 @@ class AppGeneratorTest < Rails::Generators::TestCase
     end
   end
 
+  def test_generated_environments_file_for_auto_explain
+    run_generator [destination_root, "--skip-active-record"]
+    %w(development test production).each do |env|
+      assert_file "config/environments/#{env}.rb" do |file|
+        assert_no_match %r(auto_explain_threshold_in_seconds), file
+      end
+    end
+  end
+
 protected
 
   def action(*args, &block)