We’re researching the use of Python and mod_wsgi running under apache for developing some extensive web applications.  Here are some notes on a performance test that we recently ran.
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Server:

x86_64
Python 3.1.1
mod_wsgi 3.0c5
apache 2.2
RHEL 5.3
quad core xenon
8 GB ram

Development system – not in production use.

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Application:

1 import time
2
3 def application(environ, start_response):
4     status = ‘200 OK’
5
6     output = “hello world!”
7
8     #time.sleep(1)
9
10     response_headers = [
11         (‘Content-type’, ‘text/plain’),
12         (‘Content-Length’, str(len(output))),
13         ]
14
15     start_response(status, response_headers)
16
17     return [output]

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Apache Configuration:

WSGISocketPrefix run/wsgi
<VirtualHost *>
ServerName shankproject.jason.star.ionzoft.net
DocumentRoot /home/jason/Code/ShankProject/Web
WSGIScriptAlias /Admin /home/jason/Code/ShankProject/WSGI/
Admin.wsgi
WSGIDaemonProcess shankproject.jason.star.ionzoft.net threads=15
WSGIProcessGroup shankproject.jason.star.ionzoft.net
</VirtualHost>

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Tests:

—————————————————–
# Baseline with one process and 15 threads
# 15 threads total

threads=15
no process definition

WITHOUT time.sleep(1)
concurrency = 1  >> 1800 / second
concurrency = 100 >> 3900 / second

WITH time.sleep(1)
concurrency = 1  >> 1 / second
concurrency = 100  >> 14 / second

—————————————————–
# Get a marginal improvement by doubling the threads to 30
# 30 threads total

threads=30
no process definition

WITHOUT time.sleep(1)
concurrency = 1  >> 1680 / second
concurrency = 100 >> 3500 / second

WITH time.sleep(1)
concurrency = 1  >> 1 / second
concurrency = 100  >> 30 / second

—————————————————–
# Take processes from 1 to 3
# 90 threads total

threads=30
processes=3

WITHOUT time.sleep(1)
concurrency = 1  >> 1770 / second
concurrency = 100 >> 3500 / second

WITH time.sleep(1)
concurrency = 1  >> 1 / second
concurrency = 100  >> 88 / second

—————————————————–
# Take processes from 3 to 6
# Take threads from 30 to 15
# 90 threads total

threads=30
processes=3

WITHOUT time.sleep(1)
concurrency = 1  >> 1550 / second
concurrency = 100 >> 3300 / second

WITH time.sleep(1)
concurrency = 1  >> 1 / second
concurrency = 100  >> 88 / second

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Conclusion:

mod_wsgi performance is outstanding.  Even running slower requests, it
can still handle significant concurrency in daemon mode without any
apparent issues.

Questions:
Is there any information on the balance between more processes less
threads and more threads less processes?

Thanks!