Re: Online verification of checksums

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Michael Banck <michael(dot)banck(at)credativ(dot)de>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Asif Rehman <asifr(dot)rehman(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Online verification of checksums
Date: 2020-10-22 01:41:53
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On Wed, Oct 21, 2020 at 07:10:34PM +0900, Michael Paquier wrote:
> My guess is that we should be able to make use of that for base
> backups as well, but I also think that I'd rather let v13 go with more
> retries without depending on a new API layer, removing of the LSN
> check altogether. Thinking of it, that's actually roughly what I
> posted here, but without the PageGetLSN() bit in the refactored code.
> So I see a pretty good argument to address the stable branches with
> that, and study for the future a better API to govern them all:

So, I was sleeping on this one, and I could not find a reason why we
should not address both the zero case and the random data case at the
same time, as mentioned here:

We cannot trust the fields fields of the page header because these may
have been messed up with some random corruption, so what really
matters is that the checksums don't match, and that we can just rely
on that. The zero-only case of a page is different because these
don't have a checksum set, so I would finish with something like the
attached to make the detection more robust. This does not make the
detection perfect as there is no locking insurance (we really need to
do that but v13 has been released already), but with a sufficient
number of retries this can make things much more reliable than what's

Are there any comments? Anybody?

Attachment Content-Type Size
checksums-zeros-v7.patch text/x-diff 13.1 KB

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