Re: Block-level CRC checks

Tom Lane wrote:
> Bruce Momjian <bruce@momjian.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@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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