Re: Feature: POSIX Shared memory support

Attached is a beta of the POSIX shared memory layer. It is 75% the
original sysv_shmem.c code. I'm looking for ways to refactor it down
a bit, while changing as little of the tried-and-tested code as
possible. I though I'd put it out there for comments.

Of course, unfortunately it is more complicated than the original as
it uses both sets of API. Also, I haven't tested the crash recovery
thoroughly. The POSIX code could be used Windows-style (i.e. no
crash recovery) if one ifdef'd out the SysV calls properly, if they
had such a POSIX-only platform they needed to run Postgres on.

Using both API is certainly not ideal. You mentioned,

> We've speculated on occasion about using file locking in some form
> as a
> substitute mechanism for detecting this, but that seems to just bring
> its own set of not-too-portable assumptions

What sort of file locking did you have in mind? Do you think this
might be worth me trying?

Thanks for your help,
Chris Marcellino