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From: Tom Lane <[email protected]>
To: Andres Freund <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Daniel Gustafsson <[email protected]>
Cc: Kyotaro Horiguchi <[email protected]>
Cc: [email protected]
Cc: Ibrar Ahmed <[email protected]>
Cc: [email protected]
Cc: hlinnaka <[email protected]>
Cc: Masahiko Sawada <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Daniel Wood <[email protected]>
Subject: Re: Corruption during WAL replay
Date: Fri, 25 Mar 2022 09:49:34 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CA+Tgmoa_TAJsUnFWzTevg=FzgXFyiHLJAY_L-jMDA=mH=ytysg@mail.gmail.com>
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Andres Freund <[email protected]> writes:
> On 2022-03-25 01:38:45 -0400, Tom Lane wrote:
>> AFAICS, this strategy of whacking a predetermined chunk of the page with
>> a predetermined value is going to fail 1-out-of-64K times.

> Yea. I suspect that the way the modifications and checksumming are done are
> actually higher chance than 1/64k. But even it actually is 1/64k, it's not
> great to wait for (#animals * #catalog-changes) to approach a decent
> percentage of 1/64k.

Exactly.

> I'm was curious whether there have been similar issues in the past. Querying
> the buildfarm logs suggests not, at least not in the pg_checksums test.

That test has only been there since 2018 (b34e84f16).  We've probably
accumulated a couple hundred initial-catalog-contents changes since
then, so maybe this failure arrived right on schedule :-(.

> We really ought to find a way to get to wider checksums :/

That'll just reduce the probability of failure, not eliminate it.

			regards, tom lane

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