Increased from 30 to 40 the maximum connections from a service

This is not really justified by anything, but 30 seemed small and from
tests on my machine 40 do not cause any problem. The only service
using these many connections is CWS, and having too many users per CWS
might create pool exhausted errors.

Also added a couple of warning in AWS in case there are too many users
per CWS.

Author: stefano-maggiolo

cms/db/__init__.py

@@ -3,7 +3,7 @@
 
 # Contest Management System - http://cms-dev.github.io/
 # Copyright © 2010-2012 Giovanni Mascellani <mascellani@poisson.phc.unipi.it>
-# Copyright © 2010-2014 Stefano Maggiolo <s.maggiolo@gmail.com>
+# Copyright © 2010-2015 Stefano Maggiolo <s.maggiolo@gmail.com>
 # Copyright © 2010-2012 Matteo Boscariol <boscarim@hotmail.com>
 # Copyright © 2013 Bernard Blackham <bernard@largestprime.net>
 # Copyright © 2013 Luca Wehrstedt <luca.wehrstedt@gmail.com>
@@ -83,7 +83,7 @@
 
 
 engine = create_engine(config.database, echo=config.database_debug,
-                       pool_size=20, pool_recycle=120)
+                       pool_size=20, max_overflow=20, pool_recycle=120)
 
 
 from .session import Session, ScopedSession, SessionGen, \

cms/server/templates/admin/contest.html

@@ -5,6 +5,14 @@
   <h1>Contest information</h1>
 </div>
 
+{% if len(config.contest_listen_port) > 0 %}
+  {% set ratio = round(len(contest.users) * 1.0 / len(config.contest_listen_port), 2) %}
+  {% if ratio >= 40 %}
+    At the moment, you have {{ ratio }} users for each ContestWebServer, on average.<br/>
+    A CWS can handle 40 simultaneous request. This situation might cause many requests to fail.
+  {% end %}
+{% end %}
+
 <!-- We use "multipart/form-data" to have Tornado distinguish between missing and empty values. -->
 <form enctype="multipart/form-data" action="{{ url_root }}/contest/{{ contest.id }}" method="POST" name="edit_contest">
   <table class="sub_table">

cms/server/templates/admin/userlist.html

@@ -4,6 +4,15 @@
 <div class="core_title">
   <h1>Users list</h1>
 </div>
+
+{% if len(config.contest_listen_port) > 0 %}
+  {% set ratio = round(len(contest.users) * 1.0 / len(config.contest_listen_port), 2) %}
+  {% if ratio >= 40 %}
+    At the moment, you have {{ ratio }} users for each ContestWebServer, on average.<br/>
+    A CWS can handle 40 simultaneous request. This situation might cause many requests to fail.
+  {% end %}
+{% end %}
+
 <a href="{{ url_root }}/add_user/{{ contest.id }}">Add a new user</a>
 <table class="bordered">
   <thead>