Horton

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

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Sutou Kouhei <kou@clear-code.com>
Cc: david.g.johnston@gmail.com, tgl@sss.pgh.pa.us, zhjwpku@gmail.com, michael@paquier.xyz, pgsql-hackers@postgresql.org
Date: 2025-03-25T00:45:10Z
Lists: pgsql-hackers 
On Wed, Mar 19, 2025 at 6:25 PM Sutou Kouhei <kou@clear-code.com> wrote:
>
> Hi,
>
> In <CAKFQuwaMAFMHqxDXR=SxA0mDjdmntrwxZd2w=nSruLNFH-OzLw@mail.gmail.com>
>   "Re: Make COPY format extendable: Extract COPY TO format implementations" on Wed, 19 Mar 2025 17:49:49 -0700,
>   "David G. Johnston" <david.g.johnston@gmail.com> wrote:
>
> >> And could someone help (take over if possible) writing a
> >> document for this feature? I'm not good at writing a
> >> document in English... 0009 in the attached v37 patch set
> >> has a draft of it. It's based on existing documents in
> >> doc/src/sgml/ and *.h.
> >>
> >>
> > I haven't touched the innards of the structs aside from changing
> > programlisting to synopsis.  And redoing the two section opening paragraphs
> > to better integrate with the content in the chapter opening.
> >
> > The rest I kinda went to town on...
>
> Thanks!!! It's very helpful!!!
>
> I've applied your patch. 0009 is only changed.

FYI I've implemented an extension to add JSON Lines format as a custom
COPY format[1] to check the usability of the COPY format APIs. I think
that the exposed APIs are fairly simple and minimum. I didn't find the
deficiency and excess of exposed APIs for helping extensions but I
find that it would be better to describe what the one-row callback
should do to utilize the abstracted destination. For example, in order
to use CopyToStateFlush() to write out to the destination, extensions
should write the data to cstate->fe_msgbuf. We expose
CopyToStateFlush() but not for any functions to write data there such
as CopySendString(). It was a bit inconvenient to me but I managed to
write the data directly there by #include'ing copyto_internal.h.

Regards,

[1] https://github.com/MasahikoSawada/pg_copy_jsonlines

--
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.