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From: Aleksander Alekseev <[email protected]>
To: Frits Hoogland <[email protected]>
Cc: [email protected]
Subject: Re: The ability of postgres to determine loss of files of the main fork
Date: Tue, 30 Sep 2025 18:55:16 +0300
Message-ID: <CAJ7c6TMYvYBQpgv8k+4QnajqPcroOzrj7d3snBBTKX4tHQfVYw@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Hi Frits,

> Therefore, I would like to request an enhancement: add an option to
> verify_heapam() that causes the primary key index to be scanned and makes
> sure that all line pointers in the index point to existing tuples.

I'm a bit puzzled by your emphasis on primary keys. In Postgres it is
legal to have tables without PKs, indexes, or even columns:

=# create table my_table();
=# select * from my_table;

To clarify, are you proposing not to check such tables?

> An alternative might be to track the number of segments of a relation in
> pg_class, but that may be difficult to make crash-safe.

Hm... the fact that we have a segment on disk doesn't mean it is not
empty or not corrupted. Let's say we will add a check you are
proposing. The next person will complain that we don't check the size
of the segments. The next one - about the fact that we don't verify
checksums.

So IMO there is little value in adding a check for the existence of
the segments for a single table. And the *real* check will not differ
much from something like SELECT * FROM my_table, or from making a
complete backup of the database.

-- 
Best regards,
Aleksander Alekseev

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