Re: Bug in amcheck?

From: Mihail Nikalayeu <mihailnikalayeu(at)gmail(dot)com>
To: Konstantin Knizhnik <knizhnik(at)garret(dot)ru>
Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Bug in amcheck?
Date: 2025-11-02 12:27:00
Message-ID: CADzfLwU+8dMq4EQ3kRuDCv2giS+_AUX5Q4LYO6x5PKghdAfK6A@mail.gmail.com
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Hello!

> I wonder if we should add P_ISHALFDEAD(opaque) for child page?

I am not a btree expert, but things I was able to find so far:

In commit d114cc538715e14d29d6de8b6ea1a1d5d3e0edb4 next check is added:

> bt_child_highkey_check(state, downlinkoffnum,
> child, topaque->btpo_level);

At the same time there is a comment below:

> * We go ahead with our checks if the child page is half-dead. It's safe
> * to do so because we do not test the child's high key, so it does not
> * matter that the original high key will have been replaced by a dummy
> * truncated high key within _bt_mark_page_halfdead(). All other page
> * items are left intact on a half-dead page, so there is still something
> * to test.

So, yes, it looks like we need to skip the child's high key test for
half-dead pages.

BWT, have you tried to create an injection_point-based reproducer?

Best regards,
Mikhail.

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