[mod_python] mod_python executing old versions of my code

Peter Sanchez pjs at packet-addiction.org
Thu Jan 26 18:14:03 EST 2006

I have been a little slow on this thread. This is something I had  
planned on emailing the list about myself.

I have a page hosted using mod_python.publisher (mod_python version  
3.2.5b) The page returns results from a PSP formatted template  
system. On a lot of pages I use a variable named "info_msg"

Say I login to an account, info_msg is set to 'You have logged in.'  
Go to a new page, info_msg isn't used, but the template page does  
reference it (in case it was used) and you see 'You have logged in' I  
have been trying to figure it out, but no such luck. I just found  
this thread :)

As for the "MaxRequestsPerChild 1" work around. How big of a  
performance hit does this give? Seems like it would slow things down  
a bit. The site I run is pretty busy.

When will 3.2.6 be available?



On Jan 25, 2006, at 11:50 PM, Mike Looijmans wrote:

> Graham Dumpleton wrote:
>> On 26/01/2006, at 5:40 PM, Mike Looijmans wrote:
>>> When faced with the reload problem a few years ago, I created a  
>>> special "reload" request. The request would list all the .py[oc]  
>>> files in the script folder, and tries to unload or reload() each  
>>> of them.
>> Will not work for mod_python.publisher in mod_python 3.2 and possibly
>> not at all in future versions of mod_python, but for mod_python <=  
>> 3.1.4,
>> it is better to iterate over modules in sys.modules and if they  
>> contain
>> the attribute "__mtime__" set it to 0. By doing this, it will  
>> cause the
>> mod_python importer to reload it automatically the next time it is  
>> accessed.
>> By doing it this way, you don't expose yourself to issues that  
>> might arise
>> from mixing "apache.import_module()" and "reload()".
> I was not mixing - I was using "import" exclusively. I also wasn't  
> using publisher, but I wrote my own. (this was about 4 years ago)
> "My" publisher could detect changes in the handlers, but not in the  
> sub-modules they imported. 90% of code changes only affected the UI  
> parts which were in the headers.
> The fix was there to get changes in the library modules to become  
> effective, without having to log in on the apache machine.
>>> As a result, the "main" modules as well as dependent modules will  
>>> have been reloaded or removed (At least, the ones that came from  
>>> my project - it would not make sense to unload modules like 'os').
>> Other projects should really be run in the context of a different  
>> interpreter
>> by specifying PythonInterpreter. On that basis, you would have to  
>> be selective
>> if above method used.
> There were no other projects on that server...
>>> So just sending "http://myhost/pu/reload" to the server would  
>>> cause the next request to get all new scripts.
>> This is only guaranteed to work if you are using mod_python on  
>> Win32 platform.
>> It most definitely will not work with "prefork" on UNIX and  
>> usually not on
>> "worker" on UNIX. The reason the latter will not work reliably is  
>> that there
>> can be multiple Apache child processes and your request will only  
>> hit one of
>> those child processes. You would have to hit reload many times and  
>> even then
>> you wouldn't know for sure it had been done in all of the children.
> True.
> I was using Apache 2.0.something and Solaris 2.6 at the time (had  
> to compile everything, no binary distributions), but I already  
> forced apache to use a single-process multi-threading worker.  
> Benchmarks showed no real difference with the prefork mpm. The  
> machine was seriously limited by memory, and the childs would take  
> up >12 MB of memory each, most of which could be shared. Putting it  
> into threading mode solved the memory hogging, and also had  
> advantages in caching stuff in simple dictionaries in memory. I  
> also did DB connection pooling, but after implementing and doing  
> some benchmarks, there was no real performance advantage in doing  
> it on the MySQL database, which is amazingly fast in setting up  
> connections.
> Getting this to work on a prefork system is indeed quite a  
> challenge...
> But at the time, it was a much better option than restarting an  
> Apache server process when hundreds of machines are using it...
> --
> Mike Looijmans
> Philips Natlab / Topic Automation
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