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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <bruce@momjian.us>
cc: "David G. Johnston" <david.g.johnston@gmail.com>,
        "zhoushulin1992@gmail.com" <zhoushulin1992@gmail.com>,
        "pgsql-docs@lists.postgresql.org" <pgsql-docs@lists.postgresql.org>
Subject: Re: 'pg_global' cannot be used as default_tablespace.
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Comments: In-reply-to Bruce Momjian <bruce@momjian.us>
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Bruce Momjian <bruce@momjian.us> writes:
> On Wed, Nov  1, 2023 at 06:32:37PM -0400, Tom Lane wrote:
>> But it *is* permissible, unless we add code to reject it during
>> SET as Bruce mentioned.  Which seems fairly pointless to me.  It's not
>> like there is anything unclear about the CREATE TABLE error message.

> Yeah, from the report I thought something bad happened if you tried to
> use it and that is why we had to document it.  By documenting it we are
> just giving the user advice before they get the error.  I wrote up this
> minimal patch which might have the right level of detail to avoid
> errors, if people think this is useful.

I think this will lead to just as much confusion, because people
will read it and expect that SET will fail.

If we need to document any more than we have now, we should point
out in the CREATE TABLE man page that you can't create a table in
the pg_global tablespace.  That will cover both this case and the
case of trying to select pg_global explicitly in the CREATE.

Another idea could be to adjust this bit in manage-ag.sgml:

   Two tablespaces are automatically created when the database cluster
   is initialized.  The
-  <literal>pg_global</literal> tablespace is used for shared system catal=
ogs. The
+  <literal>pg_global</literal> tablespace is used for shared system catal=
ogs,
+  and cannot be used for user-defined tables. The
   <literal>pg_default</literal> tablespace is the default tablespace of t=
he

			regards, tom lane