Subject: Re: [patch] Fix checksum verification in base backups for zero page
 headers
To: Michael Paquier <michael@paquier.xyz>
Cc: Michael Banck <michael.banck@credativ.de>,
 PostgreSQL Development <pgsql-hackers@postgresql.org>
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 <423deac52479a40624e775e6d2ab41c4e9f5b19f.camel@credativ.de>
 <20201007081852.GC30037@paquier.xyz>
 <608f3476-0598-2514-2c03-e05c7d2b0cbd@postgrespro.ru>
 <20201020062432.GA30362@paquier.xyz>
 <69b38451-e91f-95fc-c3ce-06eb778d36e0@postgrespro.ru>
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 <20201022230008.GK1475@paquier.xyz> <20201026011315.GA2973@paquier.xyz>
From: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Message-ID: <ce25a60e-bd70-6554-1e8f-7e4dc9f6ce59@postgrespro.ru>
Date: Tue, 27 Oct 2020 22:56:23 +0300
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On 26.10.2020 04:13, Michael Paquier wrote:
> On Fri, Oct 23, 2020 at 08:00:08AM +0900, Michael Paquier wrote:
>> Yeah, we could try to make the logic a bit more complicated like
>> that.  However, for any code path relying on a page read without any
>> locking insurance, we cannot really have a lot of trust in any of the
>> fields assigned to the page as this could just be random corruption
>> garbage, and the only thing I am ready to trust here a checksum
>> mismatch check, because that's the only field on the page that's
>> linked to its full contents on the 8k page.  This also keeps the code
>> simpler.
> A small update here.  I have extracted the refactored part for
> PageIsVerified() and committed it as that's independently useful.
> This makes the patch proposed here simpler on HEAD, leading to the
> attached.
> --
> Michael

Thank you for committing the first part.

In case you need a second opinion on the remaining patch, it still looks 
good to me.

-- 
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company