From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Fix table rewrites that include a column without a
 default.
In-reply-to: <20191010205903.tj73q3qcyfft3izz@alap3.anarazel.de>
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 <3328.1570740683@sss.pgh.pa.us>
 <20191010205903.tj73q3qcyfft3izz@alap3.anarazel.de>
Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Thu, 10 Oct 2019 13:59:03 -0700"
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Date: Thu, 10 Oct 2019 17:16:08 -0400
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Andres Freund <andres@anarazel.de> writes:
> On 2019-10-10 16:51:23 -0400, Tom Lane wrote:
>> Do you *really* need an event trigger to test this?

> No. I added it to avoid the tests getting "accidentally" optimized away,
> the next time somebody adds some ALTER TABLE optimizations. The fast
> default stuff had removed coverage from a test that'd have uncovered
> this bug. And an event trigger seemed to be the easiest way to achieve
> that.

> The only real alternative I can see to just removing the trigger is
> embedding a check in the trigger that will cause it to only work in the
> current session.  Something like SET regress.log_table_rewrites, and a
> IF current_setting('regress.log_table_rewrites')::bool in the function.

If you just want to verify that a rewrite happened or didn't happen,
seems like you could check whether the table's relfilenode changed.

regression=3D# select relfilenode as oldfilenode from pg_class where relna=
me =3D 'rewrite_test'
regression-# \gset
regression=3D# select relfilenode !=3D :oldfilenode as changed from pg_cla=
ss where relname =3D 'rewrite_test';
 changed =

---------
 f
(1 row)
regression=3D# alter table rewrite_test alter column notempty3_norewrite t=
ype bigint;
ALTER TABLE
regression=3D# select relfilenode !=3D :oldfilenode as changed from pg_cla=
ss where relname =3D 'rewrite_test';
 changed =

---------
 t
(1 row)

I really really don't want an event trigger running in everything that
runs in parallel with alter_table.  That's a debugging nightmare of
monster proportions.

			regards, tom lane