Add connection reset and verification upon each connection checkout

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -261,12 +261,17 @@ module ActiveRecord
       def checkout_new_connection
         c = new_connection
         @connections << c
-        @checked_out << c
-        c
+        checkout_and_verify(c)
       end
 
       def checkout_existing_connection
         c = (@connections - @checked_out).first
+        checkout_and_verify(c)
+      end
+
+      def checkout_and_verify(c)
+        c.reset!
+        c.verify!(verification_timeout)
         @checked_out << c
         c
       end

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -103,14 +103,23 @@ module ActiveRecord
         @active = false
       end
 
+      # Reset the state of this connection, directing the DBMS to clear
+      # transactions and other connection-related server-side state. Usually a
+      # database-dependent operation; the default method simply executes a
+      # ROLLBACK and swallows any exceptions which is probably not enough to
+      # ensure the connection is clean.
+      def reset!
+        execute "ROLLBACK" rescue nil
+      end
+
       # Returns true if its safe to reload the connection between requests for development mode.
       # This is not the case for Ruby/MySQL and it's not necessary for any adapters except SQLite.
       def requires_reloading?
         false
       end
 
-      # Lazily verify this connection, calling <tt>active?</tt> only if it hasn't
-      # been called for +timeout+ seconds.
+      # Lazily verify this connection, calling <tt>active?</tt> only if it
+      # hasn't been called for +timeout+ seconds.
       def verify!(timeout)
         now = Time.now.to_i
         if (now - @last_verification) > timeout

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -280,6 +280,15 @@ module ActiveRecord
         @connection.close rescue nil
       end
 
+      def reset!
+        if @connection.respond_to?(:change_user)
+          # See http://bugs.mysql.com/bug.php?id=33540 -- the workaround way to
+          # reset the connection is to change the user to the same user.
+          @connection.change_user(@config[:username], @config[:password], @config[:database])
+        else
+          super
+        end
+      end
 
       # DATABASE STATEMENTS ======================================