fsync on OSX does not actually flush the file to disk as is desired. 
This is a problem because application developers rely on fsync for file
integrity.  SQLite [1] and MySQL [2] and other major database systems
all use 'fullfsync' on OS X instead of fsync, because 'fullfsync'
provides the desired behavior.

Because the documented behavior of python's fsync function is to "force
write of file with filedescriptor to disk", I believe that on OS X the
fullfsync call should be used instead of fsync.

The supplied patch adds this functionality in a non-platform-specific
way.  It checks if there is a FULLFSYNC fcntl call available (using
"#ifdef F_FULLFSYNC", where F_FULLFSYNC is defined in sys/fcntl.h), and
if this symbol is defined then a fnctl(F_FULLFSYNC, fd, 0) is called
instead of fsync.

[1] SQLite uses fullfsync on all platforms that define it:
http://www.sqlite.org/cvstrac/fileview?f=sqlite/src/os_unix.c

[2] MySQL uses fullfsync only on the darwin platform and only when
F_FULLFSYNC is defined as 51, which seems to be short-sighted in that
this symbol may change value in future versions of OS X.  To see this
code, download a mysql 5.x source snapshot and open up
mysql-<version-number>/innobase/os/os0file.c

My patch is against trunk, but really this fix should be applied to all
versions that will have future releases.

IMO it would be better not to confuse matters my having os.fsync() call
fullfsync(); it's better to add a separate os.fullfsync() call on
platforms that support it.  That way the application can choose.  I
suppose Apple had a reason for changing the behavior...

Based on discussion in python-dev, I'm rejecting this patch.

Open a new one if you want to make F_FULLSYNC available.

Done.  See 3517
http://bugs.python.org/issue3517

On Thu, Aug 7, 2008 at 12:53 PM, Guido van Rossum
<report@bugs.python.org> wrote:
>
> Guido van Rossum <guido@python.org> added the comment:
>
> Based on discussion in python-dev, I'm rejecting this patch.
>
> Open a new one if you want to make F_FULLSYNC available.
>
> ----------
> resolution:  -> rejected
> status: open -> closed
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue3512>
> _______________________________________
>