Re: TRUNCATE on foreign table

On Thu, Apr 22, 2021 at 12:06 PM Fujii Masao
<masao.fujii@oss.nttdata.com> wrote:
> On 2021/04/22 9:39, Bharath Rupireddy wrote:
> > One comment on truncate_foreign_table_docs_v1.patch:
> > 1) I think it is "to be truncated"
> > +     <literal>rels</literal> is a list of <structname>Relation</structname>
> > +     data structures for each foreign table to truncated.
>
> Fixed. Thanks!
>
> > How about a slightly changed phrasing like below?
> > +     <literal>rels</literal> is a list of <structname>Relation</structname>
> > +     data structures of foreign tables to truncate.
> Either works at least for me. If you think that this phrasing is
> more precise or better, I'm ok with that and will update the patch again.

IMO, "rels is a list of Relation data structures of foreign tables to
truncate." looks better.

> >>> 3) How about adding an extra para(after below para in
> >>> postgres_fdw.sgml) on WHY we don't push "ONLY" to foreign tables while
> >>> truncating? We could add to the same para for other options if at all
> >>> we don't choose to push them.
> >>>     <command>DELETE</command>, or <command>TRUNCATE</command>.
> >>>     (Of course, the remote user you have specified in your user mapping must
> >>>     have privileges to do these things.)
> >>
> >> I agree to document the behavior that ONLY option is always ignored
> >> for foreign tables. But I'm not sure if we can document WHY.
> >> Because I could not find the past discussion about why ONLY option is
> >> ignored on SELECT, etc... Maybe it's enough to document the behavior?
> >
> > +1 to specify in the documentation about ONLY option is always
> > ignored.
>
> Added.
>
> > But can we specify the WHY part within deparseTruncateSql, it
> > will be there for developer reference? I feel it's better if this
> > change goes with truncate_foreign_table_dont_pass_only_clause_v2.patch
>
> I added this information into fdwhandler.sgml because the developers
> usually read fdwhandler.sgml.

Thanks!

+    <para>
+     Note that information about <literal>ONLY</literal> options specified
+     in the original <command>TRUNCATE</command> command is not passed to

I think it is not "information about", no? We just don't pass ONLY
option  instead we skip it. IMO, we can say "Note that the ONLY option
specified with a foreign table in the original TRUNCATE command is
skipped and not passed to ExecForeignTruncate."

+     <function>ExecForeignTruncate</function>.  This is the same behavior as
+     for the callback functions for <command>SELECT</command>,
+     <command>UPDATE</command> and  <command>DELETE</command> on
+     a foreign table.

How about "This behaviour is similar to the callback functions of
SELECT, UPDATE, DELETE on a foreign table"?

> >>> 4) Isn't it better to mention the "ONLY" option is not pushed to remote
> >>> -- truncate with ONLY clause
> >>> TRUNCATE ONLY tru_ftable_parent;
> >>>
> >>> TRUNCATE ONLY tru_ftable;        -- truncate both parent and child
> >>> SELECT count(*) FROM tru_ftable;   -- 0
>
> I added the comment.

LGTM.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com