open files (was Re: Virtual Hosting)

[George Toft]

My ultimate goal was to not deviate from a "standard" configuration.
I wanted the person who replaced me (I guess I knew from the beginning
that I wasn't going to stay there long) to be able to pick up a Red
Hat book and see that our systems were basically the same, with some
enhancements.  The fewer the differences, the better.

George


Kevin Buettner wrote:
> 
> On Jan 8,  8:21pm, George Toft wrote:
> 
> > > For your application, it sounds to me like you need to increase your
> > > per-process open file limit.  (You may need to increase the overall
> > > system limit too.)  I notice that as root, I'm able to do
> > > ``ulimit -n 2048'' and then ``ulimit -a'' actually shows that the limit
> > > has been increased.
> >
> > But if you exit that shell and open another, you will find your change
> > is gone - ulimit only affects the current and child shells.
> 
> True.  This means that you either need to change this ulimit value
> on a global scale or else find a way to change it in the shell that
> invokes apache.
> 
> On a Red Hat like system, you may want to take a look at the
> invocation of ulimit in /etc/rc.d/init.d/functions.  I haven't tried
> it, but I think if you change the ulimit command at this point to have
> a "-n 2048" (or some such) argument, you'll effectively change the
> ulimit for most of the processes on the system.
> 
> Of course, there's likely a more subtle way of doing this too.
> 
> > > I've done some tests (using calls to pipe()) and have determined that
> > > I'm able to create more than 1024 open files when I do this.  However,
> > > it seems to me that not all functions implemented by glibc will
> > > support more than 1024 files.  In particular, the select() function
> > > relies on the fd_set data structure to know which file descriptors to
> > > wait for.  It appears to me that you can't use this function for file
> > > descriptor numbers past 1023.  In /usr/include/bits/types.h (which is
> > > included by /usr/include/sys/types.h), I see the following:
> > >
> > >     /* Number of descriptors that can fit in an `fd_set'.  */
> > >     #define __FD_SETSIZE        1024
> > >
> > > I think you're okay if your application uses poll() instead of
> > > select() though.
> >
> > I'm not into rewriting Apache :)
> 
> Hmmm... I just took a look at the Apache source and am quite surprised
> to see that it doesn't contain any code to use poll() for those systems
> which support it.  I would've thought that this would be at least
> be a configuration option.
> 
> The other approach that you could take is to rebuild glibc with a
> different __FD_SETSIZE value.  Then rebuild Apache with the new header
> files and linked against your rebuilt glibc...
> 
> (Yes, this would be a bit of work too.)
> 
> Kevin
> 
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