Re: TRUNCATE on foreign table

At Tue, 13 Apr 2021 16:17:12 +0900, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote in
>
>
> On 2021/04/13 14:22, Kohei KaiGai wrote:
> > Let me remind the discussion at the design level.
> > If postgres_fdw (and other FDW drivers) needs to consider whether
> > ONLY-clause is given
> > on the foreign tables of them, what does a foreign table represent in
> > PostgreSQL system?
> > My assumption is, a foreign table provides a view to external data, as
> > if it performs like a table.
> > TRUNCATE command eliminates all the segment files, even if a table
> > contains multiple
> > underlying files, never eliminate them partially.
> > If a foreign table is equivalent to a table in SQL operation level,
> > indeed, ONLY-clause controls
> > which tables are picked up by the TRUNCATE command, but never controls
> > which portion of
> > the data shall be eliminated. So, I conclude that
> > ExecForeignTruncate() shall eliminate the entire
> > external data on behalf of a foreign table, regardless of ONLY-clause.
> > I think it is more significant to clarify prior to the implementation
> > details.
> > How about your opinions?
>
> I'm still thinking that it's better to pass all information including
> ONLY clause about TRUNCATE command to FDW and leave FDW to determine
> how to use them. How postgres_fdw should use the information about
> ONLY
> is debetable. But for now IMO that users who explicitly specify ONLY
> clause for
> foreign tables understand the structure of remote tables and want to
> use ONLY
> in TRUNCATE command issued by postgres_fdw. But my opinion might be
> minority,
> so I'd like to hear more opinion about this, from other developers.

From the syntactical point of view, my opinion on this is that the
"ONLY" in "TRUNCATE ONLY" is assumed to be consumed to tell to
disregard local children so it cannot be propagate further whichever
the target relation has children or not.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center