From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Sean Chittenden <sean(at)chittenden(dot)org> |
Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [PATCH] PostgreSQL 9.4 mmap(2) performance regression on FreeBSD... |
Date: | 2014-08-12 16:59:49 |
Message-ID: | 20140812165949.GA26489@awork2.anarazel.de |
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Thread: | |
Lists: | pgsql-hackers |
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.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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