Re: Detecting corrupted pages earlier

On Mon, 17 Feb 2003, Tom Lane wrote:

> Curt Sampson <cjs(at)cynic(dot)net> writes:
>
> > 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.

Well, I wasn't proposing the whole page, just the header. That would be
significantly cheaper (in fact, there's no real need even for a CRC;
probably just xoring all of the words in the header into one word would
be fine) and would tell you if the page was torn during the write, which
was what I was imagining the problem might be.

But bad memory, well, not much you can do about that beyond saying, "buy
ECC, dude."

cjs
--
Curt Sampson <cjs(at)cynic(dot)net> +81 90 7737 2974 http://www.netbsd.org
Don't you know, in this new Dark Age, we're all light. --XTC