Re: POSIX shared memory support

Stephen Frost <sfrost@snowman.net> writes:
> Finding a way for POSIX shm to do what we need, including Tom's
> concerns, without depending on SvsV shm as a crutch work around, would
> make this change much more reasonable and could be justified as moving
> to a well defined POSIX standard, and means we may be able to support
> platforms which either are new and don't implement SysV but just POSIX,
> or cases where SysV is being actively depreceated.  Neither of which is
> possible if we're stuck with using it in some cases.

Yeah, I would be far more interested in this patch if it avoided needing
SysV shmem at all.  The problem is to find an adequate substitute for
the nattch-based interlock against live children of a dead postmaster.

It's possible that file locking could be used instead, but that has its
own set of portability and reliability issues to address.  For example:
ISTR that on some NFS configurations, file locking silently doesn't
work, or might silently fail after it worked before, if the lock server
daemon should happen to crash.  And I don't even know what's available
on Windows.  So it'd need some research to make a credible proposal
along those lines.
        regards, tom lane