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From Wilfredo Sanchez <>
Subject DSO support in Rhapsody, mapped files, and other fun
Date Wed, 05 Aug 1998 17:41:07 GMT
  I'm adding DSO support to Rhapsody (ie. Mac OS X Server), and I'm looking for advice. The
problem I has is that our dynamic linker does not (yet) support the unloading of bundles.
 It seems that  
when you launch apache, the parent process reads the config, which loads all the modules.
 Then the children each fork and clear the configuration, which unloads all the modules, and
the re-reads the  
config, which reloads the modules. (This seems pretty inefficient, but that's for later.)

  Since I probably can't get the linker unload support done any time soon, I'd like not to
reload a module that's already been loaded. I can do this by caching module paths at load
time and not  
redoing ones that are already loaded. Does that seem problematic? Seems like the only time
this would really hurt is when you change a module's binary, which can be worked around by
doing a hard  
restart of the server.

  On another topic, we're trying to see what we can do with web server performance and so
we're trying to optimze the hell out of Apache since that's our shipping server. DSO support
may help  
because I've been building Apache with most of the modules turned on, since I don't want people
to have to rebuild to get features, but mod_status, and so on aren't big performance winners,
so I'm  
hoping that by only selecting modules you need, you can bump up performance some. (We also
want to provide a WebObjects module as an add-on, and don't want to make people recompile
Apache for that..)  

  So we have a MacOS 8 server that's beating out Apache on Rhapsody by a fair margin, and
we think that's gotta be nuts, and the hardware's no quite fair and so on, but still, we should
be able to  
stomp on MacOS 8 and NT, because we're cool and so on. And so, we got the network guys to
look at the network stack, and indeed, we now are a lot better, but not we're really *stomping*
on anyone, so  
we're looking harder and currently it looks like Apache is CPU bound. Now they are testing
with 1.3.0 and all those static modules, so I think we can address some of that with DSO support
and not  
configuring everything in.

  But Joe seems to think that Apache is opening a file (eg. index.html) mmap'ing it, and then
closing and unmapping it.  We're thinking that caching these mapped files would be righteously
cool, in  
that it might really bump up performance.  Joe's getting his impressions from kernel traces,
and not so much from looking at Apache code, so I'm wondering if Apache has a strategy for
caching mapped  
files and where I might look for it, or if it's something we'd have to contribute.

  I'm now working with 1.3.1, so once I get things ironed out I'll be resubmitting all of
my patches that I sent before, but against 1.3.1, if it looks like they haven't been committed.
I'll make an  
effort to break up the configure/makefile work I did before so that you don't have to fear
and loath the sheer size of it.

	Thanks for the help.

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