Hi!
We're in the process of learning GAE, and over the last two days have
hit a wall. Before going too far into the description, here's the
versions of things we're using:
* Django 1.0 beta 2
* app-engine-django-helper r58
It started yesterday; we were getting strange import errors, and only
once in a while:
----- snip -----
<class 'django.core.exceptions.ImproperlyConfigured'>: Error importing
middleware middleware.redirects: "No module named
middleware.redirects"
Traceback (most recent call last):
File "/base/data/home/apps/vendastaweb/0.39/main.py", line 88, in
<module>
main()
File "/base/data/home/apps/vendastaweb/0.39/main.py", line 58, in
real_main
util.run_wsgi_app(application)
File "/base/python_lib/versions/1/google/appengine/ext/webapp/
util.py", line 76, in run_wsgi_app
result = application(env, _start_response)
File "/base/data/home/apps/vendastaweb/0.39/django/core/handlers/
wsgi.py", line 211, in __call__
self.load_middleware()
File "/base/data/home/apps/vendastaweb/0.39/django/core/handlers/
base.py", line 40, in load_middleware
raise exceptions.ImproperlyConfigured, 'Error importing middleware
%s: "%s"' % (mw_module, e)
----- snip -----
Hitting refresh a few times would make the error go away. These
errors weren't consistent; it would just be some random module from
our project that would fail to import.
We also started noticing that we were getting messages like:
This request used a high amount of CPU, and was roughly 8.2 times over
the average request CPU limit. High CPU requests have a small quota,
and if you exceed this quota, your app will be temporarily disabled.
So, of course, the answer is to profile. Profiling is where it got
really wierd. Our execution of "real_main()" was a small fraction
(about 1/3) of the request time measured by GAE, and most of *that*
time was occupied by "__import__":
----- snip -----
: 80216 function calls (76826 primitive calls) in
0.580 CPU seconds
:
: Ordered by: internal time
: List reduced from 1040 to 30 due to restriction <30>
:
: ncalls tottime percall cumtime percall
filename:lineno(function)
: 7 0.108 0.015 0.120 0.017
{google3.apphosting.runtime._apphosting_runtime___python__apiproxy.Wait}
: 48/42 0.060 0.001 0.351 0.008 {__import__}
: 1 0.060 0.060 0.183 0.183 /base/data/
home/apps/vendastaweb/0.29/vendastaweb/models/feed.py:5(<module>)
: 1 0.022 0.022 0.071 0.071 /base/data/
home/apps/vendastaweb/0.29/vendastaweb/views/faces.py:5(<module>)
: 456/98 0.022 0.000 0.072 0.001 /base/
python_dist/lib/python2.5/sre_parse.py:385(_parse)
----- snip -----
Our models (feed, for example) are incredibly simple, and it makes no
sense that they'd take any significant amount of CPU time to create
the class.
The profiling log entries (from the admin panel) look like this
(trimmed up a bit):
----- snip -----
09-10 04:54PM 41.119 /projects/ 200 1482ms 8kb
71.17.167.74 - - [10/09/2008:16:54:42 -0700] "GET /projects/ HTTP/1.1"
200 8091 - -
Profile data:
Function time:
118854 function calls (114692 primitive calls) in 0.638 CPU
seconds
Ordered by: internal time
List reduced from 1178 to 30 due to restriction <30>
----- snip -----
To further confuse things, I uploaded the application in parallel, and
the parallel copy seems to run flawlessly (no timeouts, no quota
violations, etc). I've hit both of them with httperf (from 1-5 conn/
sec), and the parallel copy succeeds 100% of the time, while the
original copy fails ~30-40% of the time.
Please let me know if I've missed anything relevant.
Cheers
Tony
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