Re: TRUNCATE on foreign tables

Hello,

The attached patch adds TRUNCATE support on foreign table.

This patch adds an optional callback ExecForeignTruncate(Relation rel)
to FdwRoutine.
It is invoked during ExecuteTruncateGuts, then FDW driver hands over
the jobs related
to complete "truncate on the foreign table".
Of course, it is not clear to define the concept of "truncate" on some
FDW drivers.
In this case, TRUNCATE command prohibits to apply these foreign tables.

2019 is not finished at everywhere on the earth yet, so I believe it
is Ok to add this patch
to CF-2020:Jan.

Best regards,

2020年1月1日(水) 11:46 Kohei KaiGai <kaigai(at)heterodb(dot)com>:
>
> Hello,
>
> We right now don't support TRUNCATE on foreign tables.
> It may be a strange missing piece and restriction of operations.
> For example, if a partitioned table contains some foreign tables in its leaf,
> user cannot use TRUNCATE command to clean up the partitioned table.
>
> Probably, API design is not complicated. We add a new callback for truncate
> on the FdwRoutine, and ExecuteTruncateGuts() calls it if relation is foreign-
> table. In case of postgres_fdw, it also issues "TRUNCATE" command on the
> remote side in the transaction block [*1].
>
> [*1] But I hope oracle_fdw does not follow this implementation as is. :-)
>
> How about your thought?
>
> I noticed this restriction when I'm working on Arrow_Fdw enhancement for
> "writable" capability. Because Apache Arrow [*2] is a columnar file format,
> it is not designed for UPDATE/DELETE, but capable to bulk-INSERT.
> It is straightforward idea to support only INSERT, and clear data by TRUNCATE.
>
> [*2] Apache Arrow - https://arrow.apache.org/docs/format/Columnar.html
>
> Best regards,
> --
> HeteroDB, Inc / The PG-Strom Project
> KaiGai Kohei <kaigai(at)heterodb(dot)com>

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