Stress that you should really install the C-based MySQL library when running on the pure Ruby one (closes #9507)

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@7521 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -49,6 +49,11 @@ def self.require_mysql
         rescue LoadError => cannot_require_mysql
           # Use the bundled Ruby/MySQL driver if no driver is already in place
           begin
+            ActiveRecord::Base.logger.info(
+              "WARNING: You're using the Ruby-based MySQL library that ships with Rails. This library is not suited for production. " +
+              "Please install the C-based MySQL library instead (gem install mysql)."
+            ) if ActiveRecord::Base.logger
+
             require 'active_record/vendor/mysql'
           rescue LoadError
             raise cannot_require_mysql

railties/configs/databases/mysql.yml

@@ -3,7 +3,7 @@
 # Install the MySQL driver:
 #   gem install mysql
 # On MacOS X:
-#   gem install mysql -- --include=/usr/local/lib
+#   sudo gem install mysql -- --with-mysql-dir=/usr/local/mysql
 # On Windows:
 #   gem install mysql
 #       Choose the win32 build.