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From: Pavel Borisov <pashkin.elfe@gmail.com>
Date: Wed, 24 Jun 2026 14:44:35 +0400
Message-ID: 
 <CALT9ZEE9O6eMdj3fPH+g67zMPNWe3PEhZ69wnOOnb2NfO-jBgw@mail.gmail.com>
Subject: Re: Add SPLIT PARTITION/MERGE PARTITIONS commands
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>,
 Dmitry Koval <d.koval@postgrespro.ru>,
	Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers@lists.postgresql.org,
	Tomas Vondra <tomas.vondra@enterprisedb.com>,
 Alvaro Herrera <alvherre@alvh.no-ip.org>
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Hi, Alexander!

On Wed, 24 Jun 2026 at 14:25, Alexander Korotkov <aekorotkov@gmail.com> wro=
te:
>
> On Mon, Jun 22, 2026 at 1:44=E2=80=AFPM Pavel Borisov <pashkin.elfe@gmail=
.com> wrote:
> > On Sun, 21 Jun 2026 at 16:11, Alexander Korotkov <aekorotkov@gmail.com>=
 wrote:
> > >
> > > On Thu, Jun 18, 2026 at 6:49=E2=80=AFPM Justin Pryzby <pryzby@telsaso=
ft.com> wrote:
> > > > On Thu, Jun 18, 2026 at 10:31:11AM +0300, Alexander Korotkov wrote:
> > > > > Pushed with your suggestions accepted.
> > > >
> > > > Thanks.  When I went back to test this, I merged ~25 partitions tha=
t
> > > > were all on the same tablespace, but the merged table was created o=
n the
> > > > default tablespace.
> > > >
> > > > I tried again with default_tablespace set, but it was ignored.  I t=
hink
> > > > that's wrong.  It's good to follow the tablespace of the parent tab=
le,
> > > > but if it has no tablespace set, default_tablespace should be obeye=
d.
> > > > See surrounding logic in DefineRelation.
> > > >
> > > > I see the docs say this:
> > > > +       <command>ALTER TABLE MERGE PARTITION</command> uses the par=
titioned
> > > > +       table itself as the template to construct the new partition=
.
> > > > +       The new partition will inherit the same table access method=
, persistence
> > > > +       type, and tablespace as the partitioned table.
> > >
> > > Correct, please see the attached patch, it makes
> > > createPartitionTable() deal with tablespaces the same was as
> > > DefineRelation() does.
> >
> > Thank you for working on this feature!
> > I've looked into the last v1 patch.
> >
> > Does it also worth inheriting DefineRelation()'s check and error for
> > the case if (tablespaceId =3D=3D GLOBALTABLESPACE_OID)?
> > A brief look for default_tablespace GUC doesn't reveal a way why it
> > could not be set to global tablespace in a session.
>
> Thank you for catching this.  I've added this check and corresponding tes=
ts.

Looked at the patch v2.
I think in test we'd better split comments for the failing block (SET
default_tablespace TO pg_global;) and for the successful block (after
RESET default_tablespace;). Otherwise, the comment paragraph looks a
little hard to read to me:
+-- Parent has no explicit tablespace and default_tablespace is empty: the
+-- new partition uses the database default (reltablespace =3D 0).  Also
+-- exercise the pg_global rejection path with default_tablespace pointing
+-- at the shared tablespace.

Overall the patch looks good to me.

Regards,
Pavel Borisov
Supabase