mod_python is actually going away too, and they're recommending wsgi
instead.

Christian

-- 
Christian Hammond - chip...@chipx86.com
Review Board - http://www.reviewboard.org
VMware, Inc. - http://www.vmware.com


On Tue, Oct 5, 2010 at 9:53 PM, David Trowbridge <trowb...@gmail.com> wrote:

> I'm glad you figured it out!
>
> As far as what to do now, from what I've heard, the future is more
> likely to involve wsgi than fastcgi. I think it's a little better with
> regards to memory leaks, too.
>
> -David
>
>
>
> On Tue, Oct 5, 2010 at 9:43 PM, mxbraun <matthew.br...@intel.com> wrote:
> >
> >> 5) Anyone have any suggestions as to how to proceed with debugging
> >> this, aside from rolling up my sleeves, and tucking in with GDB?
> >
> > So, I rolled up my sleeves, and tucked in with GDB...The problem
> > proved to be the issue documented here at the Django project under the
> > section, "If you get a segmentation fault":
> > http://docs.djangoproject.com/en/dev/howto/deployment/modpython/
> >
> > httpd loads mod_php, which loads in a PHP extension containing MySQL
> > bindings to the system's (single-threaded?) mysql library: /usr/lib64/
> > libmysqlclient.so.15.  Because OpenSuSE is such an old system, this
> > library implements the ABI for MySQL major number/version 15, or in
> > other words, the libmysqlclient library uses version 15 of the data
> > structures when talking to the server.  Specifically, the MYSQL_FIELD
> > structure occupies 120 bytes on a 64-bit system.
> >
> > mod_python--which can and does reside in the same httpd process as
> > mod_php--loads up Reviewboard, Django, and the python bindings for
> > MySQL, along with its own version of a MySQL library.  However, the
> > python-mysql package which shipped with OpenSuSE 10.3 is too old to
> > work with the version of Django that Reviewboard 1.x line needs.  As
> > such, we have to build a new python-mysql from source, either using
> > easy_install, or manually (which was easier to debug).
> >
> > However, on this particular system, in spite of the elderly/stale
> > nature of the OS, the local IT group has installed a not-quite-as-
> > creaky version of MySQL--specifically one which implements version 16
> > of the data structures--not version 15.  (This change was introduced
> > in mid 2007: http://lists.mysql.com/commits/31791 .) The result of
> > this is that when we build python-mysql, we wind up building python
> > bindings to a library which uses Version 16 of the data structures,
> > and functions.  This library's Version 16 definition of the
> > MYSQL_FIELD struct is 128 bytes on a 64-bit system--8 more bytes than
> > it was in version 15, thanks to an "extension" pointer, which should
> > help preserve binary compatibility.
> >
> > The MySQL server is sufficiently backward-compatible  to understand
> > both version 15 and version 16 data structures and queries.  The
> > problem comes in when mod_python and mod_php are both dynamically
> > loaded into the same httpd process.  They both load in their own mysql
> > libraries, and this causes some sort of problem.  There must be some
> > shared state or persistence which is causing the queries in the
> > Version 16 library to receive Version 15 responses.
> >
> > Ultimately, we see a segmentation fault in strlen because (for some
> > reason) we get a Version 15 response to a Version 16
> > mysql_real_query() call in MySQL-python.  This result is an array of
> > Version 15 MYSQL_FIELD structs (120-bytes apiece) being processed by
> > Version 16 code, which expects each of these structs to occupy 128
> > bytes. This misalignment of structure boundaries eventually leads to a
> > non-pointer being interpreted as a pointer which is fed to strlen, and
> > when that happens, it all falls down.
> >
> > It seems like I have a few options here:
> > 1) Use fastcgi instead of mod_python, and take my chances with memory
> > leaks.
> > 2) Rebuild mod_php with MySQL bindings that use the same Version16
> > library as mod_python does.  Because the two modules should then use
> > the same libraries, the problem should go away...in theory...
> > 3) Try to rebuild MySQL-python with the version 15 library and header
> > files.
> > 4) Try something like mod_wsgi.
> >
> > Most likely I'm going to go with #1--it should work, and I have the
> > existing system to use as an example for configuration, etc, which is
> > a bonus. #2 means building more stuff at the risk of breaking things
> > that are currently working, since we do serve PHP pages from this
> > system. #3 seems more Frankenstein-y to me than I have time for (and
> > the storm's not at its height, anyway...), and #4 is uninteresting
> > since I'm currently waaayy behind schedule.
> >
> > Perhaps this advice in the Reviewboard Documentation should be
> > amended, if not reconsidered:
> >        "If you’re using Apache, we highly recommend using mod_python, as
> > fastcgi has been known to have memory leak issues with Review Board."
> > 1) As of June 17th, mod_python is officially dead.
> >
> http://blog.dscpl.com.au/2010/06/modpython-project-is-now-officially.html
> > Shouldn't RB recommend an actively-maintained piece of software? While
> > the code and documentation for mod_python are available, the FAQ,
> > which allegedly describes this problem, and who knows, maybe even a
> > few solutions--that'd be nice--in detail, is not. The mailing list
> > archives for this project have been basically silent for the past few
> > months as well.  Decay has set in, there, and will only increase.
> > 2) It would probably be useful to echo Django's warning about
> > combining mod_python with mod_php, when using MySQL as a backend.
> > Basically, if you're not serving PHP with this web server, you should
> > be able to disable mod_php, and have mod_python work just fine.
> > (That's what I should have done to quickly confirm that this was the
> > problem.)
> >
> > Thanks,
> >
> > m@
> >
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