Skip site navigation (1) Skip section navigation (2)

Re: Block-level CRC checks

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Block-level CRC checks
Date: 2009-12-01 22:12:13
Message-ID: 200912012212.nB1MCDr16266@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > OK, crazy idea #3.  What if we had a per-page counter of the number of
> > hint bits set --- that way, we would only consider a CRC check failure
> > to be corruption if the count matched the hint bit count on the page.
> 
> Seems like rather a large hole in the ability to detect corruption.
> In particular, this again assumes that you can accurately locate all
> the hint bits in a page whose condition is questionable.  Pick up the
> wrong bits, you'll come to the wrong conclusion --- and the default
> behavior you propose here is the wrong result.

I was assuming any update of hint bits would update the per-page counter
so it would always be accurate.  However, I seem to remember we don't
lock the page when updating hint bits, so that wouldn't work.

-- 
  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. +

In response to

pgsql-hackers by date

Next:From: Greg StarkDate: 2009-12-01 22:13:20
Subject: Re: Block-level CRC checks
Previous:From: Greg SmithDate: 2009-12-01 22:05:25
Subject: Re: [CORE] EOL for 7.4?

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group