| From: | Michael Paquier <michael(at)paquier(dot)xyz> |
|---|---|
| To: | Magnus Hagander <magnus(at)hagander(dot)net> |
| Cc: | Michael Banck <michael(dot)banck(at)credativ(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Asif Rehman <asifr(dot)rehman(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, David Steele <david(at)pgmasters(dot)net>, Stephen Frost <sfrost(at)snowman(dot)net> |
| Subject: | Re: Online verification of checksums |
| Date: | 2020-11-20 07:28:01 |
| Message-ID: | 20201120072801.GF8506@paquier.xyz |
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| Lists: | pgsql-hackers |
On Mon, Nov 16, 2020 at 11:41:51AM +0100, Magnus Hagander wrote:
> I was referring to the latest patch on the thread. But as I said, I have
> not read up on all the different issues raised in the thread, so take it
> with a big grain os salt.
>
> And I would also echo the previous comment that this code was adapted from
> what the pgbackrest folks do. As such, it would be good to get a comment
> from for example David on that -- I don't see any of them having commented
> after that was mentioned?
Agreed. I am adding Stephen as well in CC. From the code of
backrest, the same logic happens in src/command/backup/pageChecksum.c
(see pageChecksumProcess), where two checks on pd_upper and pd_lsn
happen before verifying the checksum. So, if the page header finishes
with random junk because of some kind of corruption, even corrupted
pages would be incorrectly considered as correct if the random data
passes the pd_upper and pg_lsn checks :/
--
Michael
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