Re: BUG #16045: vacuum_db crash and illegal memory alloc after pg_upgrade from PG11 to PG12

Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> On Wed, Oct 09, 2019 at 07:18:45PM -0400, Tom Lane wrote:
>> Fortunately, there should be close to zero people with user tables
>> depending on sql_identifier. I think we should just add a test in
>> pg_upgrade that refuses to upgrade if there are any such columns.
>> It won't be the first such restriction.

> Hmmm, yeah. I agree the number of people using sql_identifier in user
> tables is low, but OTOH we got this report within a week after release,
> so maybe it's higher than we think.

True.

> Another option would be to teach pg_upgrade to switch the columns to
> 'text' or 'varchar', not sure if that's possible or how much work would
> that be.

I think it'd be a mess --- the actual hacking would have to happen in
pg_dump, I think, and it'd be a kluge because pg_dump doesn't normally
understand what server version its output is going to. So we'd more
or less have to control it through a new pg_dump switch that pg_upgrade
would use. Ick.

Also, even if we did try to silently convert such columns that way,
I bet we'd get other bug reports about "why'd my columns suddenly
change type?". So I'd rather force the user to be involved.

regards, tom lane