Horton

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

Masahiko Sawada <sawada.mshk@gmail.com>

View thread View on postgr.es
From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Sutou Kouhei <kou@clear-code.com>
Cc: michael@paquier.xyz, david.g.johnston@gmail.com, tgl@sss.pgh.pa.us, zhjwpku@gmail.com, pgsql-hackers@postgresql.org
Date: 2025-07-13T18:28:16Z
Lists: pgsql-hackers

Attachments

On Mon, Jun 30, 2025 at 3:00 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Wed, Jun 25, 2025 at 4:35 PM Sutou Kouhei <kou@clear-code.com> wrote:
> >
> > Hi,
> >
> > In <CAD21AoC19fV5Ujs-1r24MNU+hwTQUeZMEnaJDjSFwHLMMdFi0Q@mail.gmail.com>
> >   "Re: Make COPY format extendable: Extract COPY TO format implementations" on Wed, 25 Jun 2025 00:48:46 +0900,
> >   Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > >> >> It's natural to add more related APIs with this
> > >> >> approach. The single registration API provides one feature
> > >> >> by one operation. If we use the RegisterCopyRoutine() for
> > >> >> FROM and TO formats API, it's not natural that we add more
> > >> >> related APIs. In this case, some APIs may provide multiple
> > >> >> features by one operation and other APIs may provide single
> > >> >> feature by one operation. Developers may be confused with
> > >> >> the API. For example, developers may think "what does mean
> > >> >> NULL here?" or "can we use NULL here?" for
> > >> >> "RegisterCopyRoutine("new-format", NewFormatFromRoutine,
> > >> >> NULL)".
> > >> >
> > >> > We can document it in the comment for the registration function.
> > >>
> > >> I think that API that can be understandable without the
> > >> additional note is better API than API that needs some
> > >> notes.
> > >
> > > I don't see much difference in this case.
> >
> > OK. It seems that we can't agree on which API is better.
> >
> > I've implemented your idea as the v42 patch set. Can we
> > proceed this proposal with this approach? What is the next
> > step?
>
> I'll review the patches.

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.

The patch is a very PoC phase and we would need to scrutinize the
fields that should or should not be exposed. Feedback is very welcome.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com

Commits

  1. Refactor Copy{From|To}GetRoutine() to use pass-by-reference argument.

  2. Refactor COPY FROM to use format callback functions.

  3. Refactor COPY TO to use format callback functions.

  4. Another try to fix BF failure introduced in commit ddd5f4f54a.

  5. Revert "Refactor CopyReadAttributes{CSV,Text}() to use a callback in COPY FROM"

  6. Improve COPY TO performance when server and client encodings match

  7. Simplify signature of CopyAttributeOutCSV() in copyto.c

  8. Revert "Refactor CopyAttributeOut{CSV,Text}() to use a callback in COPY TO"

  9. Refactor CopyAttributeOut{CSV,Text}() to use a callback in COPY TO

  10. Refactor CopyReadAttributes{CSV,Text}() to use a callback in COPY FROM

  11. Add progress reporting of skipped tuples during COPY FROM.

  12. pgbench: Add \syncpipeline

  13. meson: Make gzip and tar optional

  14. Export the external file reader used in COPY FROM as APIs.