Re: pg_dump is broken for partition tablespaces

Hi,

On 2019-03-06 19:45:06 +1300, David Rowley wrote:
> Over on [1] Andres pointed out that the pg_dump support for the new to
> PG12 tablespace inheritance feature is broken. This is the feature
> added in ca4103025dfe26 to allow a partitioned table to have a
> tablespace that acts as the default tablespace for newly attached
> partitions. The idea being that you can periodically change the
> default tablespace for new partitions to a tablespace that sits on a
> disk partition with more free space without affecting the default
> tablespace for normal non-partitioned tables. Anyway...

I'm also concerned that the the current catalog representation isn't
right. As I said:

> I also find it far from clear that:
> <listitem>
> <para>
> The <replaceable class="parameter">tablespace_name</replaceable> is the name
> of the tablespace in which the new table is to be created.
> If not specified,
> <xref linkend="guc-default-tablespace"/> is consulted, or
> <xref linkend="guc-temp-tablespaces"/> if the table is temporary. For
> partitioned tables, since no storage is required for the table itself,
> the tablespace specified here only serves to mark the default tablespace
> for any newly created partitions when no other tablespace is explicitly
> specified.
> </para>
> </listitem>
> is handled correctly. The above says that the *specified* tablespaces -
> which seems to exclude the default tablespace - is what's going to
> determine what partitions use as their default tablespace. But in fact
> that's not true, the partitioned table's pg_class.retablespace is set to
> what default_tablespaces was at the time of the creation.

I still think the feature as is doesn't seem to have very well defined
behaviour.

> If we instead did:
>
> CREATE TABLE public.listp1 (a integer
> );
>
> ALTER TABLE public.list1 ATTACH PARTITION public.listp FOR VALUES IN (1);

Isn't that a bit more expensive, because now the table needs to be
scanned for maching the value? That's probably neglegible though, given
it'd probably always empty.

Greetings,

Andres Freund