On Feb 6, 8:57 am, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > On Feb 5, 12:52 pm, John Nagle <[EMAIL PROTECTED]> wrote: > > > > > [EMAIL PROTECTED] wrote: > > > John Nagle wrote: > > > >>Graham Dumpleton wrote: > > > >>>On Feb 4, 1:05 pm, Paul Rubin <http://[EMAIL PROTECTED]> wrote: > > > >>>>"Paul Boddie" <[EMAIL PROTECTED]> writes: > > >> Realistically,mod_pythonis a dead end for large servers, > > >>because Python isn't really multi-threaded. The Global Python > > >>Lock means that a multi-core CPU won't help performance. > > > > The GIL doesn't affect seperate processes, and any large server that > > > cares about stability is going to be running a pre-forking MPM no > > > matter what language they're supporting. > > > Pre-forking doesn't reduce load; it just improves responsiveness. > > You still pay for loading all the modules on every request. > > No, you don't. Each server is persistent and serves many requests-- > it's not at all like CGI, and it reuses the loaded Python image. > > So if you have, say, an expensive to load Python module, that will > only be executed once for each server you start...e.g. if you have > Apache configured to accept up to 50 connections, the module will be > run at most 50 times; once each of the 50 processes has started up, > they stick around until you restart Apache, unless you've configured > apache to only serve X requests in one process before restarting it. > (The one major feature thatmod_python_is_ missing is the ability to > do some setup in the Python module prior to forking. That would make > restarting Apache somewhat nicer).
There would be a few issues with preloading modules before the main Apache child process performed the fork. The first is whether it would be possible for code to be run with elevated privileges given that the main Apache process usually is started as root. I'm not sure at what point it switches to the special user Apache generally runs as and whether in the main process the way this switch is done is enough to prevent code getting back root privileges in some way, so would need to be looked into. The second issue is that there can be multiple Python interpreters ultimately created depending on how URLs are mapped, thus it isn't just an issue with loading a module once, you would need to create all the interpreters you think might need it and preload it into each. All this will blow out the memory size of the main Apache process. There is also much more possibility for code, if it runs up extra threads, to interfere with the operation of the Apache parent process. One particular area which could be a problem is where Apache wants to do a restart, as it will attempt to unload the mod_python module and reload it. Right now this may not be an issue as mod_python does the wrong thing and doesn't shutdown Python allowing it to be reinitialised when mod_python is reloaded, but in mod_wsgi (when mod_python isn't also being loaded), it will shutdown Python. If there is user code executing in a thread within the parent process this may actually stop mod_wsgi from cleanly shutting down Python thus causing Apache to hang. All up, the risks of loading extra modules in the parent process aren't worth it and could just result in things being less stable. Graham -- http://mail.python.org/mailman/listinfo/python-list
