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. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
