Re: [PATCH] Generic type subscripting

> On 19 September 2017 at 10:21, Arthur Zakirov <a(dot)zakirov(at)postgrespro(dot)ru>
wrote:
> On Mon, Sep 18, 2017 at 12:25:04PM +0200, Dmitry Dolgov wrote:
>> > I think it would be good to add new catalog table. It may be named as
>> pg_type_sbs or pg_subscripting (second is better I think).
>> > This table may have the fields:
>> > - oid
>> > - sbstype
>> > - sbsinit
>> > - sbsfetch
>> > - sbsassign
>>
>> What is `sbstype`?
>
>'sbstype' is oid of type from pg_type for which subscripting is created.
I.e. pg_type may not have the 'typsubsparse' field.

I'm confused, why do we need it? I mean, isn't it enough to have a
subscripting
oid in a pg_type record?

> On 18 September 2017 at 12:25, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
wrote:
>
> Overall I have only one concern about this suggestion - basically it
changes
> nothing from the perspective of functionality or implementation quality.

Few more thoughts about this point. Basically if we're going this way (i.e.
having `pg_subscripting`) there will be one possible change of
functionality -
in this case since we store oids of all the required functions, we can pass
them to a `parse` function (so that a custom extension does not need to
resolve
them every time).

At the same time there are consequences of storing `pg_subscripting`, e.g.:

* I assume the performance would be worse because we have to do more
actions to
actually call a proper function.

* The implementation itself will be little bit more complex I think.

* Should we think about other functionality besides `CREATE` and `DROP`, for
example `ALTER` (as far as I see aggregations support that).

and maybe something else that I don't see now.