Re: TRUNCATE on foreign table

On Thu, Apr 8, 2021 at 6:47 PM Bharath Rupireddy <
bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:

> On Thu, Apr 8, 2021 at 6:44 PM Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>
> wrote:
> > The followings are the open items and discussion points that I'm
> thinking of.
> >
> > 1. Currently the extra information (TRUNCATE_REL_CONTEXT_NORMAL,
> TRUNCATE_REL_CONTEXT_ONLY or TRUNCATE_REL_CONTEXT_CASCADING) about how a
> foreign table was specified as the target to truncate in TRUNCATE command
> is collected and passed to FDW. Does this really need to be passed to FDW?
> Seems Stephen, Michael and I think that's necessary. But Kaigai-san does
> not. I also think that TRUNCATE_REL_CONTEXT_CASCADING can be removed
> because there seems no use case for that maybe.
>
> I think we should remove the unused enums/macros, instead we could
> mention a note of the extensibility of those enums/macros in the
> comments section around the enum/macro definitions.
>
> > 2. Currently when the same foreign table is specified multiple times in
> the command, the extra information only for the foreign table found first
> is collected. For example, when "TRUNCATE ft, ONLY ft" is executed,
> TRUNCATE_REL_CONTEXT_NORMAL is collected and _ONLY is ignored because "ft"
> is found first. Is this OK? Or we should collect all, e.g., both _NORMAL
> and _ONLY should be collected in that example? I think that the current
> approach (i.e., collect the extra info about table found first if the same
> table is specified multiple times) is good because even local tables are
> also treated the same way. But Kaigai-san does not.
>
> IMO, the foreign truncate command should be constructed by collecting
> all the information i.e. "TRUNCATE ft, ONLY ft" and let the remote
> server execute how it wants to execute. That will be consistent and no
> extra logic is required to track the already seen foreign tables while
> foreign table collection/foreign truncate command is being prepared on
> the local server.
>
> I was thinking that the postgres throws error or warning for commands
> such as truncate, vaccum, analyze when the same tables are specified,
> but seems like that's not what it does.
>
> > 3. Currently postgres_fdw specifies ONLY clause in TRUNCATE command that
> it constructs. That is, if the foreign table is specified with ONLY,
> postgres_fdw also issues the TRUNCATE command for the corresponding remote
> table with ONLY to the remote server. Then only root table is truncated in
> remote server side, and the tables inheriting that are not truncated. Is
> this behavior desirable? Seems Michael and I think this behavior is OK. But
> Kaigai-san does not.
>
> I'm okay with the behaviour as it is consistent with what ONLY does to
> local tables. Documenting this behaviour(if not done already) is a
> better way I think.
>
> > 4. Tab-completion for TRUNCATE should be updated so that also foreign
> tables are displayed.
>
> It will be good to have.
>
> With Regards,
> Bharath Rupireddy.
> EnterpriseDB: http://www.enterprisedb.com

w.r.t. point #1:
bq. I think we should remove the unused enums/macros,

I agree. When there is more concrete use case which requires new enum, we
can add enum whose meaning would be clearer.

Cheers