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

Hi Kou,

I tried to follow the thread but had to skip quite some discussions in the middle part of the thread. From what I read, it appears to me that there were a lot of back-and-forth discussions on the specific implementation details (i.e. do not touch existing format implementation), performance concerns and how to split the patches to make it more manageable.

My understanding is that the provided v17 patch aims to achieve the followings:
- Retain existing format implementations as built-in formats, and do not go through the new interface for them.
- Make sure that there is no sign of performance degradation.
- Refactoring the existing code to make it easier and possible to make copy handlers extensible. However, some of the infrastructure work that are required to make copy handler extensible are intentionally delayed for future patches. Some of the work were proposed as patches in earlier messages, but they were not explicitly referenced in recent messages.

Overall, the current v17 patch applies cleanly to HEAD. “make check-world” also runs cleanly. If my understanding of the current status of the patch is correct, the patch looks good to me.

Regards,
Yong