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

Hi,

On 2025-07-14 03:28:16 +0900, Masahiko Sawada wrote:
> I've reviewed the 0001 and 0002 patches. The API implemented in the
> 0002 patch looks good to me, but I'm concerned about the capsulation
> of copy state data. With the v42 patches, we pass the whole
> CopyToStateData to the extension codes, but most of the fields in
> CopyToStateData are internal working state data that shouldn't be
> exposed to extensions. I think we need to sort out which fields are
> exposed or not. That way, it would be safer and we would be able to
> avoid exposing copyto_internal.h and extensions would not need to
> include copyfrom_internal.h.
>
> I've implemented a draft patch for that idea. In the 0001 patch, I
> moved fields that are related to internal working state from
> CopyToStateData to CopyToExectuionData. COPY routine APIs pass a
> pointer of CopyToStateData but extensions can access only fields
> except for CopyToExectuionData. In the 0002 patch, I've implemented
> the registration API and some related APIs based on your v42 patch.
> I've made similar changes to COPY FROM codes too.

I've not followed the development of this patch - but I continue to be
concerned about the performance impact it has as-is and the amount of COPY
performance improvements it forecloses.

This seems to add yet another layer of indirection to a lot of hot functions
like CopyGetData() etc.

Greetings,

Andres Freund