On 2014-10-11 20:33:57 -0400, Bruce Momjian wrote: > On Tue, Aug 12, 2014 at 07:08:06PM -0400, Robert Haas wrote: > > On Tue, Aug 12, 2014 at 12:59 PM, Andres Freund <and...@2ndquadrant.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?
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. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
