| 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 |
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| 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. +
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