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Re: pgsql: Improve wording.

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Martijn van Oosterhout <kleptog(at)svana(dot)org>
Subject: Re: pgsql: Improve wording.
Date: 2007-12-22 05:19:23
Message-ID: 200712220519.lBM5JND26496@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
bruce wrote:
> > I think your proposed wording is removed enough from what the
> > complainant was saying that it is not worth to stick it in.  The point
> > here is, to what extent do we want to spoon-feed careless sysadmins?
> 
> OK, I have removed the paratheses paragraph about fork() and added link
> to an article about the OOM:
> 
>     http://lwn.net/Articles/104179/
> 
>     On Linux 2.6 and later, an additional measure is to modify the
>     kernel's behavior so that it will not <quote>overcommit</> memory.
>     Although this setting will not prevent the <ulink
>     url="http://lwn.net/Articles/104179/">OOM killer</> from being invoked
>     altogether, it will lower the chances significantly and will therefore
>     lead to more robust system behavior.  This is done by selecting strict
>     overcommit mode via <command>sysctl</command>:

I just read that article in full and it does a better job of explaining
OOM than we ever could: :-)

    Not everybody agrees that this (OOM) is a fruitful use of developer time.
    Andries Brouwer came up with this analogy:
	
	An aircraft company discovered that it was cheaper to fly its planes
	with less fuel on board. The planes would be lighter and use less fuel
	and money was saved. On rare occasions however the amount of fuel was
	insufficient, and the plane would crash. This problem was solved by the
	engineers of the company by the development of a special OOF
	(out-of-fuel) mechanism. In emergency cases a passenger was selected and
	thrown out of the plane. (When necessary, the procedure was repeated.) A
	large body of theory was developed and many publications were devoted to
	the problem of properly selecting the victim to be ejected. Should the
	victim be chosen at random? Or should one choose the heaviest person? Or
	the oldest? Should passengers pay in order not to be ejected, so that
	the victim would be the poorest on board? And if for example the
	heaviest person was chosen, should there be a special exception in case
	that was the pilot? Should first class passengers be exempted? Now that
	the OOF mechanism existed, it would be activated every now and then, and
	eject passengers even when there was no fuel shortage. The engineers are
	still studying precisely how this malfunction is caused.


-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://postgres.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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