Re: Make COPY format extendable: Extract COPY TO format implementations

On Fri, Dec 15, 2023 at 12:45 PM Sutou Kouhei <kou@clear-code.com> wrote:
>
> Hi,
>
> In <CAEG8a3JuShA6g19Nt_Ejk15BrNA6PmeCbK7p81izZi71muGq3g@mail.gmail.com>
>   "Re: Make COPY format extendable: Extract COPY TO format implementations" on Fri, 15 Dec 2023 11:27:30 +0800,
>   Junwang Zhao <zhjwpku@gmail.com> wrote:
>
> >> > Adding a prefix or suffix would be one option but to give extensions
> >> > more flexibility, another option would be to support format = 'custom'
> >> > and add the "handler" option to specify a copy handler function name
> >> > to call. For example, COPY ... FROM ... WITH (FORMAT = 'custom',
> >> > HANDLER = 'arrow_copy_handler').
> >>
> > I like the prefix/suffix idea, easy to implement. *custom* is not a FORMAT,
> > and user has to know the name of the specific handler names, not
> > intuitive.
>
> Ah! I misunderstood this idea. "custom" is the special
> format to use "HANDLER". I thought that we can use it like
>
>    (FORMAT = 'arrow', HANDLER = 'arrow_copy_handler_impl1')
>
> and
>
>    (FORMAT = 'arrow', HANDLER = 'arrow_copy_handler_impl2')
>
> .
>
> >> Interesting. If we use this option, users can choose an COPY
> >> FORMAT implementation they like from multiple
> >> implementations. For example, a developer may implement a
> >> COPY FROM FORMAT = 'json' handler with PostgreSQL's JSON
> >> related API and another developer may implement a handler
> >> with simdjson[1] which is a fast JSON parser. Users can
> >> choose whichever they like.
> > Not sure about this, why not move Json copy handler to contrib
> > as an example for others, any extensions share the same format
> > function name and just install one? No bound would implement
> > another CSV or TEXT copy handler IMHO.
>
> I should have used a different format not JSON as an example
> for easy to understand. I just wanted to say that extension
> developers can implement another implementation without
> conflicting another implementation.

Yeah, I can see the value of the HANDLER option now. The possibility
of two extensions for the same format using same hanlder name should
be rare I guess ;)
>
>
> Thanks,
> --
> kou



--
Regards
Junwang Zhao