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Re: Block-level CRC checks

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>
Cc: Aidan Van Dyk <aidan(at)highrise(dot)ca>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Brian Hurt <bhurt(at)janestcapital(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2008-10-02 17:38:06
Message-ID: 200810021738.m92Hc6815139@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Jonah H. Harris wrote:
> On Thu, Oct 2, 2008 at 1:07 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> >> If we're double-buffering the write, I don't see where we could be
> >> introducing a torn-page, as we'd actually be writing a copied version
> >> of the buffer.  Will look into this.
> >
> > The torn page is during kernel write to disk, I assume, so it is still
> > possible.
> 
> Well, we can't really control too much of that.  The most common
> solution to that I've seen is to double-write the page (which some
> OSes already do regardless).  Or, are you meaning something else?

I just don't see how writing a copy of the page (rather than the
original) to the kernel affects issues about torn pages.

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

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

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