Re: [PATCH] Improve amcheck to also check UNIQUE constraint in btree index.

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From: Pavel Borisov <[email protected]>
To: Mark Dilger <[email protected]>
Cc: Alexander Korotkov <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Noah Misch <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Cc: Aleksander Alekseev <[email protected]>
Cc: Postgres hackers <[email protected]>
Cc: Maxim Orlov <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Greg Stark <[email protected]>
Cc: Julien Rouhaud <[email protected]>
Cc: David Steele <[email protected]>
Cc: Peter Geoghegan <[email protected]>
Cc: Maxim Orlov <[email protected]>
Cc: [email protected]
Subject: Re: [PATCH] Improve amcheck to also check UNIQUE constraint in btree index.
Date: Fri, 17 May 2024 23:42:42 +0400
Message-ID: <CALT9ZEEJs33i2u_vGUFdubw7y_C92HPyNuwfS5uYS+71XmJEgw@mail.gmail.com> (raw)
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Hi, Mark!

On Fri, 17 May 2024 at 23:10, Mark Dilger <[email protected]>
wrote:

>
>
> > On May 17, 2024, at 11:51 AM, Pavel Borisov <[email protected]>
> wrote:
> >
> > Amcheck with checkunique option does check uniqueness violation between
> pages. But it doesn't warranty detection of cross page uniqueness
> violations in extremely rare cases when the first equal index entry on the
> next page corresponds to tuple that is not visible (e.g. dead). In this, I
> followed the Peter's notion [1] that checking across a number of dead equal
> entries that could theoretically span even across many pages is an unneeded
> code complication and amcheck is not a tool that provides any warranty when
> checking an index.
>
> This confuses me a bit.  The regression test creates a table and index but
> never performs any DELETE nor any UPDATE operations, so none of the index
> entries should be dead.  If I am understanding you correct, I'd be forced
> to conclude that the uniqueness checking code is broken.  Can you take a
> look?
>
At the first glance it's not clear to me:
- why your test creates cross-page unique constraint violations?
- how do you know they are not detected?

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