Re: TRUNCATE on foreign table

2021年3月30日(火) 2:54 Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>:
>
> On 2021/03/29 13:55, Michael Paquier wrote:
> > On Mon, Mar 29, 2021 at 10:53:14AM +0900, Fujii Masao wrote:
> >> I understand the motivation of this. But the other DMLs like UPDATE also
> >> do the same thing for foreign tables? That is, when those DML commands
> >> are executed on foreign tables, their changes are WAL-logged in a publisher side,
> >> e.g., for logical replication? If not, it seems strange to allow only TRUNCATE
> >> on foreign tables to be WAL-logged in a publisher side...
> >
> > Executing DMLs on foreign tables does not generate any WAL AFAIK with
> > the backend core code, even with wal_level = logical, as the DML is
> > executed within the FDW callback (see just ExecUpdate() or
> > ExecInsert() in nodeModifyTable.c), and foreign tables don't have an
> > AM set as they have no physical storage. A FDW may decide to generate
> > some WAL records by itself though when doing the opeation, using the
> > generic WAL interface but that's rather limited.
> >
> > Generating WAL for the truncation of foreign tables sounds also like a
> > strange concept to me. I think that you should just make the patch
> > work so as the truncation is passed down to the FDW that decides what
> > it needs to do with it, and do nothing more than that.
>
> Agreed.
>
Ok, it's fair enough.

Best regards,
--
HeteroDB, Inc / The PG-Strom Project
KaiGai Kohei <kaigai(at)heterodb(dot)com>