Re: Shared Memory: How to use SYSV rather than MMAP ?

On Thu, Dec 27, 2018 at 7:25 AM Andres Freund <andres@anarazel.de> wrote:
> On December 26, 2018 6:48:31 PM GMT+01:00, Robert Haas <robertmhaas@gmail.com> wrote:
> >I disagree.  I think there is a growing body of evidence that
> >b0fc0df9364d2d2d17c0162cf3b8b59f6cb09f67 killed performance on many
> >types of non-Linux systems.  This is the first report I recall about
> >AIX, but there have been previous complaints about some BSD variants.
>
> Exactly. I think we should have added this a few years ago.

I added a commitfest entry for this.

The 0001 patch (shared_memory_type GUC, code written by Andres, with a
first swing at documentation by me) seems close to committable, but as
Tom pointed out, there is a documentation burden here, and I'm
planning to go through and make sure that other relevant sections
explain the situation clearly.  I don't propose to change the default
on any platform.  It's a shame that it's still advantageous to use
clunky sysv facilities on some systems, but so long as that is the
case, it's good to be able to reach that; it's also good to have a
reasonable default that doesn't require any sysctl changes, so I think
this is a good thing to have as a GUC and mmap should be the default.

For the 0002 patch (essentially what Tony asked for, except made to
respect the huge_pages GUC by me, untested), I hope Tony or another
AIX user will be able to help get this into the right shape.  The main
idea there is that the default setting huge_pages=try should use large
pages if the OS is configured to support that, but otherwise fall back
to regular pages (just as we do on Linux and Windows).

-- 
Thomas Munro
http://www.enterprisedb.com