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Re: Posix Shared Mem patch

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: Magnus Hagander <magnus(at)hagander(dot)net>, pgsql-hackers(at)postgresql(dot)org, Robert Haas <robertmhaas(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>
Subject: Re: Posix Shared Mem patch
Date: 2012-06-28 18:11:18
Message-ID: 383.1340907078@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On Thursday, June 28, 2012 08:00:06 PM Tom Lane wrote:
>> Well, the permissions angle is actually a good thing here.  There is
>> pretty much no risk of the mlock succeeding on a box that hasn't been
>> specially configured --- and, in most cases, I think you'd need root
>> cooperation to raise postgres' RLIMIT_MEMLOCK.  So I think we could try
>> to mlock without having any effect for 99% of users.  The 1% who are
>> smart enough to raise the rlimit to something suitable would get better,
>> or at least more predictable, performance.

> The heightened limit might just as well target at another application and be 
> setup a bit to widely. I agree that it is useful, but I think it requires its 
> own setting, defaulting to off. Especially as there are no experiences with 
> running a larger pg instance that way.

[ shrug... ]  I think you're inventing things to be afraid of, and
ignoring a very real problem that mlock could fix.

			regards, tom lane

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