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

Sutou Kouhei <kou@clear-code.com>

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From: Sutou Kouhei <kou@clear-code.com>
To: jian.universality@gmail.com
Cc: michael@paquier.xyz, andres@anarazel.de, sawada.mshk@gmail.com, zhjwpku@gmail.com, andrew@dunslane.net, nathandbossart@gmail.com, pgsql-hackers@postgresql.org
Date: 2024-03-11T00:56:24Z
Lists: pgsql-hackers 
Hi,

In <CACJufxEgn3=j-UWg-f2-DbLO+uVSKGcofpkX5trx+=YX6icSFg@mail.gmail.com>
  "Re: Make COPY format extendable: Extract COPY TO format implementations" on Mon, 11 Mar 2024 08:00:00 +0800,
  jian he <jian.universality@gmail.com> wrote:

> Hi, here are my cents:
> Currently in v17, we have 3 extra functions within DoCopyTo
> CopyToStart, one time, start, doing some preliminary work.
> CopyToOneRow, doing the repetitive work, called many times, row by row.
> CopyToEnd, one time doing the closing work.
> 
> seems to need a function pointer for processing the format and other options.
> or maybe the reason is we need a one time function call before doing DoCopyTo,
> like one time initialization.

I know that JSON format wants it but can we defer it? We can
add more options later. I want to proceed this improvement
step by step.

More use cases will help us which callbacks are needed. We
will be able to collect more use cases by providing basic
callbacks.

> generally in v17, the code pattern looks like this.
> if (cstate->opts.binary)
> {
> /* handle binary format */
> }
> else if (cstate->routine)
> {
> /* custom code, make the copy format extensible */
> }
> else
> {
> /* handle non-binary, (csv or text) format */
> }
> maybe we need another bool flag like `bool buildin_format`.
> if the copy format is {csv|text|binary}  then buildin_format is true else false.
> 
> so the code pattern would be:
> if (cstate->opts.binary)
> {
> /* handle binary format */
> }
> else if (cstate->routine && !buildin_format)
> {
> /* custom code, make the copy format extensible */
> }
> else
> {
> /* handle non-binary, (csv or text) format */
> }
> 
> otherwise the {CopyToRoutine| CopyFromRoutine} needs a function pointer
> to distinguish native copy format and extensible supported format,
> like I mentioned above?

Hmm. I may miss something but I think that we don't need the
bool flag. Because we don't set cstate->routine for native
copy formats. So we can distinguish native copy format and
extensible supported format by checking only
cstate->routine.


Thanks,
-- 
kou

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.