Re: Detecting corrupted pages earlier

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.

			regards, tom lane