apache+mod_wsgi configuration for django project(s) on a quad core

I've been experiment quite some time with a "typical" django setting upon nginx+apache2+mod_wsgi+memcached(+postgresql) (reading the doc and some questions on SO and SF, see comments)

Since I'm still unsatisfied with the behavior (definitely because of some bad misconfiguration on my part) I would like to know what a good configuration would look like with these hypotesis:

• Quad-Core Xeon 2.8GHz
• 8 gigs memory
• several django projects (anything special related to this?)

These are excerpts form my current confs:

EDIT: I've added more stuff to make this complete but following Graham's suggestion I will follow up on the wsgi mailing list

apache 2 (>apache2 -v)

Server version: Apache/2.2.12 (Ubuntu)
Server built:   Nov 18 2010 21:16:51
Server's Module Magic Number: 20051115:23
Server loaded:  APR 1.3.8, APR-Util 1.3.9
Compiled using: APR 1.3.8, APR-Util 1.3.9
Architecture:   64-bit
Server MPM:     Worker
  threaded:     yes (fixed thread count)
    forked:     yes (variable process count)
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/worker"
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D DYNAMIC_MODULE_LIMIT=128
 -D HTTPD_ROOT=""
 -D SUEXEC_BIN="/usr/lib/apache2/suexec"
 -D DEFAULT_PIDLOG="/var/run/apache2.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="/etc/apache2/mime.types"
 -D SERVER_CONFIG_FILE="/etc/apache2/apache2.conf"

apache2 conf

PidFile ${APACHE_PID_FILE}
Timeout 60
KeepAlive Off

ServerSignature Off
ServerTokens Prod
#MaxKeepAliveRequests 100
#KeepAliveTimeout 15
# worker MPM
<IfModule mpm_worker_module>
    StartServers          2
    ServerLimit           4
    MinSpareThreads       2
    MaxSpareThreads       4
    ThreadLimit          32
    ThreadsPerChild      16
    MaxClients          64#128
    MaxRequestsPerChild   10000
</IfModule>

...

SetEnv VHOST null 
#WSGIPythonOptimize 2

<VirtualHost *:8082>
    ServerName subdomain.domain.com
    ServerAlias www.domain.com
    SetEnv VHOST subdomain.domain
    AddDefaultCharset UTF-8
    ServerSignature Off

    LogFormat "%{X-Real-IP}i %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\"" custom
    ErrorLog  /home/project1/var/logs/apache_error.log
    CustomLog /home/project1/var/logs/apache_access.log custom

    AllowEncodedSlashes On

    WSGIDaemonProcess subdomain.domain user=www-data group=www-data threads=25
    WSGIScriptAlias / /home/project1/project/wsgi.py
    WSGIProcessGroup %{ENV:VHOST}
</VirtualHost>

wsgi.py

Currently using version 3.3 built from source

import os
import sys

# setting all the right paths....


_realpath = os.path.realpath(os.path.dirname(__file__))
_public_html = os.path.normpath(os.path.join(_realpath, '../'))    

sys.path.append(_realpath)
sys.path.append(os.path.normpath(os.path.join(_realpath, 'apps')))
sys.path.append(os.path.normpath(_public_html))
sys.path.append(os.path.normpath(os.path.join(_public_html, 'libs')))
sys.path.append(os.path.normpath(os.path.join(_public_html, 'django')))


os.environ['DJANGO_SETTINGS_MODULE'] = 'settings'

import django.core.handlers.wsgi

_application = django.core.handlers.wsgi.WSGIHandler()

def application(environ, start_response):
    """
    Launches django passing over some environment (domain name) settings
    """

    application_group = environ['mod_wsgi.application_group']
    """
    wsgi application group is required. It's also used to generate the
    HOST.DOMAIN.TLD:PORT parameters to pass over
    """
    assert application_group
    fields = application_group.replace('|', '').split(':')
    server_name = fields[0]
    os.environ['WSGI_APPLICATION_GROUP'] = application_group
    os.environ['WSGI_SERVER_NAME'] = server_name
    if len(fields) > 1 :
        os.environ['WSGI_PORT'] = fields[1]
    splitted = server_name.rsplit('.', 2)    
    assert splitted >= 2
    splited.reverse()
    if len(splitted) > 0 :
        os.environ['WSGI_TLD'] = splitted[0]
    if len(splitted) > 1 :
        os.environ['WSGI_DOMAIN'] = splitted[1]
    if len(splitted) > 2 :
        os.environ['WSGI_HOST'] = splitted[2]
    return _application(environ, start_response)`

folder structure

in case it matters (slightly shortened actually)

/home/www-data/projectN/var/logs
                       /project (contains manage.py, wsgi.py, settings.py)
                       /project/apps (all the project ups are here)
                       /django
                       /libs

Please forgive me in advance if I overlooked something obvious.

My main question is about the apache2 wsgi settings. Are those fine? Is 25 threads an /ok/ number with a quad core for one only django project? Is it still ok with several django projects on different virtual hosts? Should I specify 'process'? Any other directive which I should add? Is there anything really bad in the wsgi.py file?

I've been reading about potential issues with the standard wsgi.py file, should I switch to that?

Or.. should this conf just be running fine, and I should look for issues somewhere else?

So, what do I mean by "unsatisfied": well, I often get quite high CPU WAIT; but what is worse, is that relatively often apache2 gets stuck. It just does not answer anymore, and has to be restarted. I have setup a monit to take care of that, but it ain't a real solution. I have been wondering if it's an issue with the database access (postgresql) under heavy load, but even if it was, why would the apache2 processes get stuck?

Beside these two issues, performance is overall great. I even tried New Relic and got very good average results.

edit I will not be able to provide an answer myself as I have, temporarily, moved to an nginx+gunicorn environment.

Also follow up on google groups for my personal situation and issues! Sounds like Graham is, of course, really busy (mod_wsgi is a free side project!) but moving to Read The Docs sounds great, and solving that one backlog issue would be totally awesome. That and the new Apache 2.4 might make me reconsider the best combo (currently nginx+gunicorn, then I might drop nginx for a varnish+apache+mod_wsgi setting)