Re: [PATCH] PostgreSQL 9.4 mmap(2) performance regression on FreeBSD...

On Mon, Oct 13, 2014 at 04:19:39PM +0200, Andres Freund wrote:
> On 2014-10-13 10:15:29 -0400, Robert Haas wrote:
> > On Sun, Oct 12, 2014 at 5:36 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> > > IIRC, as pointed out above, it's primarily based on a misunderstanding
> > > about when mmap is used for in dsm. I.e. that it's essentially just a
> > > fallback/toy implementation and that posix or sysv should rather be
> > > used.
> >
> > Perhaps, but I still see no reason not to apply it. It may not help
> > many people, but it won't hurt anything, either. So why not?
>
> More complicated, less tested code. For no practical benefit, it'll still
> be slower than posix shm if there's any memmory pressure. But if you
> want to apply it, go ahead, I won't cry louder than this email.
>
> I still think the mmap dsm implementation is a bad idea. We shouldn't
> put additional effort into it. If anything we should remove it.

If we have it, we should improve it, or remove it. We might want to use
this code for something else in the future, so it should be improved
where feasible.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ Everyone has their own god. +