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Re: Posix Shared Mem patch

From: Andres Freund <andres(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>
Subject: Re: Posix Shared Mem patch
Date: 2012-07-03 15:55:30
Message-ID: 201207031755.30159.andres@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tuesday, July 03, 2012 05:41:09 PM Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > Btw, RhodiumToad/Andrew Gierth on irc talked about a reason why sysv
> > shared memory might be advantageous on some platforms. E.g. on freebsd
> > there is the kern.ipc.shm_use_phys setting which prevents paging out
> > shared memory and also seems to make tlb translation cheaper. There does
> > not seem to exist an alternative for anonymous mmap.
> Isn't that mlock()?
Similar at least yes. I think it might also make the virtual/physical 
translation more direct but that ist just the impression of a very short 
search.

> > So maybe we should make that a config option?
> I'd really rather not.  If we're going to go in this direction, we
> should just go there.
I don't really care, just wanted to bring up that at least one experienced 
user would be disappointed ;). As the old implementation needs to stay around 
for EXEC_BACKEND anyway, the price doesn't seem to be too high.

Andres
-- 
Andres Freund		http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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