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From: Tom Lane <[email protected]>
To: SATYANARAYANA NARLAPURAM <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Álvaro Herrera <[email protected]>
Cc: Antonin Houska <[email protected]>
Subject: Re: [Bug]Vacuum full silently NULL out fast default columns
Date: Mon, 04 May 2026 09:40:48 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAHg+QDeoccU5CudrJpmSKZfKZ1gRMNY=5BxSC=JpHgkonzgcOw@mail.gmail.com>
References: <CAHg+QDeoccU5CudrJpmSKZfKZ1gRMNY=5BxSC=JpHgkonzgcOw@mail.gmail.com>

SATYANARAYANA NARLAPURAM <[email protected]> writes:
> VACUUM FULL silently turns columns added via ALTER TABLE ... ADD COLUMN ...
> DEFAULT <const> into NULL
> on all pre-existing rows. The issue exists for other operations like
> CLUSTER, REPACK.

That is a seriously awful bug.  Fortunately it is not in any shipping
release.  A quick bisect run agrees that it broke here:

28d534e2ae0ac888b5460f977a10cd9bb017ef98 is the first bad commit
commit 28d534e2ae0ac888b5460f977a10cd9bb017ef98 (HEAD)
Author: Álvaro Herrera <[email protected]>
Date:   Mon Apr 6 21:55:08 2026 +0200

    Add CONCURRENTLY option to REPACK

> Patch attached. Added a regression test in fast_default.sql covering
> VACUUM FULL, CLUSTER, and REPACK on a table with fast-default columns
> including a NOT NULL CHECK column.

I don't know if this is the best code fix (I don't like putting extra
checks into a loop condition like this).  But I agree we need some
more tests covering this area.

			regards, tom lane

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