From: | "Karsten Hilbert" <Karsten(dot)Hilbert(at)gmx(dot)net> |
---|---|
To: | "Adrian Klaver" <adrian(dot)klaver(at)aklaver(dot)com> |
Cc: | pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org> |
Subject: | Aw: Re: pg_dump include/exclude data, was: verify checksums / CREATE DATABASE |
Date: | 2019-06-11 18:15:34 |
Message-ID: | trinity-09990bfd-ae66-4c01-b9bb-cafb31a57e9f-1560276934383@3c-app-gmx-bs19 |
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Lists: | pgsql-general |
> > The problem I hope to protect against with this approach: the
> > CREATE DATABASE might untaint corrupted data from a bad disk
> > block into a good disk block virtue of doing a file level
> > copy.
> >
> > I hope my reasoning isn't going astray.
>
> As I understand it checksums are done on the page level using a hash(for
> details: https://doxygen.postgresql.org/checksum__impl_8h_source.html)
> I am not sure how a page could get un-corrupted by virtue of a file copy.
Ah, no, I did not explain myself well.
Let's assume a corrupted, bad (but readable at the hardware
level) disk block B. A filesystem level copy (as in CREATE
DATABASE) would successfully read that disk block B and
copy the corrupted content into a good disk block G elsewhere
on the disk. Verifying the checksum of the page sitting on
block B before doing the database cloning would
reveal the corruption before it got cloned.
Does that make sense ?
Karsten
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