Re: Re: [PATCHES] A patch for xlog.c

On Mon, 26 Feb 2001, Nathan Myers wrote:

> > 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.
>
> There are enormous advantages to avoiding the need to configure kernel
> settings. It makes PG a better citizen. PG is much easier to drop in
> and use if you don't need attention from the IT department.

Is there a reason why Oracle still uses shared memory and hasn't moved to
mmap()? Are there advantages to it that we aren't seeing, or is oracle
just too much of a mahemouth for that sort of overhaul? Don't go with the
quick answer either ...

> > Besides, what makes you think there's not a limit on the size of shmem
> > allocatable via mmap()?
>
> I've never seen any mmap limit documented. Since mmap() is how
> everybody implements shared libraries, such a limit would be equivalent
> to a limit on how much/many shared libraries are used.

There are/will be limits based on how an admin sets his/her per user
datasize limits on their OS ...