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

On Tue, Aug 12, 2014 at 07:08:06PM -0400, Robert Haas wrote:
> On Tue, Aug 12, 2014 at 12:59 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> > On 2014-08-12 09:42:30 -0700, Sean Chittenden wrote:
> >> One of the patches that I've been sitting on and am derelict in punting
> >> upstream is the attached mmap(2) flags patch for the BSDs. Is there any
> >> chance this can be squeezed in to the PostreSQL 9.4 release?
> >>
> >> The patch is trivial in size and is used to add one flag to mmap(2) calls in
> >> dsm_impl.c. Alan Cox (FreeBSD alc, not Linux) and I went back and forth
> >> regarding PostgreSQL's use of mmap(2) and determined that the following is
> >> correct and will prevent a likely performance regression in PostgreSQL 9.4.
> >> In PostgreSQL 9.3, all mmap(2) calls were called with the flags MAP_ANON |
> >> MAP_SHARED, whereas in PostgreSQL 9.4 this is not the case.
> >
> > The performancewise important call to mmap will still use that set of
> > flags, no? That's the one backing shared_buffers.
> >
> > The mmap backend for *dynamic* shared memory (aka dsm) is *NOT* supposed
> > to be used on common platforms. Both posix and sysv shared memory will
> > be used before falling back to the mmap() backend.
>
> Hmm, yeah. This might still be a good thing to do (because what do we
> lose?) but it shouldn't really be an issue in practice.

Is there a reason this was not applied?

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

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