Re: [HACKERS] pg_upgrade failed with error - ERROR: column "a" in child table must be marked NOT NULL

On Fri, Sep 29, 2023 at 09:16:35AM +0900, Michael Paquier wrote:
> You mean when upgrading from an instance of 9.6 or older as c30f177 is
> not there, right?

No - while upgrading from v15 to v16.  I'm not clear on how we upgraded
*to* v15 without hitting the issue, nor how the "not null" got
dropped...

> Anyway, it seems like the patch from [1] has no need to run this check
> when the old cluster's version is 10 or newer.  And perhaps it should
> mention that this check could be removed from pg_upgrade once v10
> support is out of scope, in the shape of a comment.

You're still thinking of PRIMARY KEY as the only way to hit this, right?
But Ali Akbar already pointed out how to reproduce the problem with DROP
NOT NULL - which still applies to both v16 and v17.