Re: BUG #17409: Unable to alter data type of clustered column which is referenced by foreign key

On Fri, 18 Feb 2022 at 00:38, Japin Li <japinli(at)hotmail(dot)com> wrote:
> On Wed, 16 Feb 2022 at 22:38, PG Bug reporting form <noreply(at)postgresql(dot)org> wrote:
>> The following bug has been logged on the website:
>>
>> Bug reference: 17409
>> Logged by: Holly Roberts
>> Email address: holly(dot)roberts(at)starlingbank(dot)com
>> PostgreSQL version: 14.2
>> Operating system: Debian 10.2.1-6
>> Description:
>>
>> When attempting to change the data type of a column that has previously been
>> clustered on, which is also referenced by a foreign key, then an exception
>> is thrown.
>>
>> Reproduction steps using a fresh database:
>> CREATE TABLE parent (
>> parent_field INTEGER CONSTRAINT pk_parent PRIMARY KEY
>> );
>> CREATE TABLE child (
>> child_field INTEGER,
>> CONSTRAINT fk_child FOREIGN KEY (child_field) REFERENCES parent
>> (parent_field)
>> );
>> CLUSTER parent USING pk_parent;
>> ALTER TABLE parent ALTER COLUMN parent_field SET DATA TYPE BIGINT;
>>
>> This throws the following error:
>> ERROR: relation 16458 has multiple clustered indexes
>> 'SELECT 16458::regclass' returns 'parent';
>> This has previously worked on various versions of postgres 12 and 13 for me
>> (latest tried 13.6)
>>
>
> It seems the following commit cause this problem.
>
> commit 8b069ef5dca97cd737a5fd64c420df3cd61ec1c9
> Author: Peter Eisentraut <peter(at)eisentraut(dot)org>
>
> Change get_constraint_index() to use pg_constraint.conindid
>
> It was still using a scan of pg_depend instead of using the conindid
> column that has been added since.
>
> Since it is now just a catalog lookup wrapper and not related to
> pg_depend, move from pg_depend.c to lsyscache.c.
>
> Reviewed-by: Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>
> Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
> Discussion: https://www.postgresql.org/message-id/flat/4688d55c-9a2e-9a5a-d166-5f24fe0bf8db%40enterprisedb.com
>
>
> After some analyze, I found `ALTER TABLE parent ALTER COLUMN parent_field SET DATA TYPE BIGINT`
> will split into `ALTER TABLE parent ALTER COLUMN parent_field SET DATA TYPE BIGINT` and
> `ALTER TABLE public.child ADD CONSTRAINT fk_child FOREIGN KEY (child_field) REFERENCES parent(parent_field)`
> statements.
>
> When the second stement executed in RememberConstraintForRebuilding(), the
> get_constraint_index() returns valid oid after 8b069ef5, however, before this
> commit, it returns invalid oid.
>
> The different is that the get_constraint_index() uses pg_depend to find
> constraint index oid before 8b069ef5, after this commit it uses lsyscache
> to find index oid.
>
> I'm not sure this is a bug or not. Any thoughts?
>
> Also Cc to Peter Eisentraut who commits this.

The RememberClusterOnForRebuilding() use the tab->clusterOnIndex to check
the cluster index exist or not, however, the cluster index can occur more
than once, so I think we should check the clustered index by index name.
Here is a patch to fix it. Any suggestions?

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.