Re: [PATCHES] A patch for xlog.c

Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> It allows no backing store on disk. It is the BSD solution to SysV
> share memory. Here are all the BSDi flags:

> MAP_ANON Map anonymous memory not associated with any specific file.
> The file descriptor used for creating MAP_ANON must be -1.
> The offset parameter is ignored.

Hmm. Now that I read down to the "nonstandard extensions" part of the
HPUX man page for mmap(), I find

If MAP_ANONYMOUS is set in flags:

o A new memory region is created and initialized to all zeros.
This memory region can be shared only with descendants of
the current process.

While I've said before that I don't think it's really necessary for
processes that aren't children of the postmaster to access the shared
memory, I'm not sure that I want to go over to a mechanism that makes it
*impossible* for that to be done. Especially not if the only motivation
is to avoid having to configure the kernel's shared memory settings.

Besides, what makes you think there's not a limit on the size of shmem
allocatable via mmap()?

regards, tom lane