Re: Detecting corrupted pages earlier

Tom Lane wrote:
> Curt Sampson <cjs@cynic.net> writes:
> > On Mon, 17 Feb 2003, Tom Lane wrote:
> >> Postgres has a bad habit of becoming very confused if the page header of
> >> a page on disk has become corrupted.
> 
> > What typically causes this corruption?
> 
> Well, I'd like to know that too.  I have seen some cases that were
> identified as hardware problems (disk wrote data to wrong sector, RAM
> dropped some bits, etc).  I'm not convinced that that's the whole story,
> but I have nothing to chew on that could lead to identifying a software
> bug.
> 
> > If it's any kind of a serious problem, maybe it would be worth keeping
> > a CRC of the header at the end of the page somewhere.
> 
> See past discussions about keeping CRCs of page contents.  Ultimately
> I think it's a significant expenditure of CPU for very marginal returns
> --- the layers underneath us are supposed to keep their own CRCs or
> other cross-checks, and a very substantial chunk of the problem seems
> to be bad RAM, against which occasional software CRC checks aren't 
> especially useful.

I believe the farthest we got was the idea of adding a CRC page
check option in case you suspected bad hardware.

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