Re: Make COPY format extendable: Extract COPY TO format implementations - Mailing list pgsql-hackers

Hi,

In <ZbyiDHIrxRgzYT99@paquier.xyz>
  "Re: Make COPY format extendable: Extract COPY TO format implementations" on Fri, 2 Feb 2024 17:04:28 +0900,
  Michael Paquier <michael@paquier.xyz> wrote:

> One idea I was considering is whether we should use a special value in
> the "format" DefElem, say "custom:$my_custom_format" where it would be
> possible to bypass the formay check when processing options and find
> the routines after processing all the options.  I'm not wedded to
> that, but attaching the routines to the state data is IMO the correct
> thing, because this has nothing to do with CopyFormatOptions.

Thanks for sharing your idea.
Let's discuss how to support custom options after we
complete the current performance changes.

>> I'm OK with the approach. But how about adding the extra
>> callbacks to Copy{From,To}StateData not
>> Copy{From,To}Routines like CopyToStateData::data_dest_cb and
>> CopyFromStateData::data_source_cb? They are only needed for
>> "text" and "csv". So we don't need to add them to
>> Copy{From,To}Routines to keep required callback minimum.
> 
> And set them in cstate while we are in the Start routine, right?

I imagined that it's done around the following part:

@@ -1418,6 +1579,9 @@ BeginCopyFrom(ParseState *pstate,
        /* Extract options from the statement node tree */
        ProcessCopyOptions(pstate, &cstate->opts, true /* is_from */ , options);
 
+       /* Set format routine */
+       cstate->routine = CopyFromGetRoutine(cstate->opts);
+
        /* Process the target relation */
        cstate->rel = rel;
 

Example1:

/* Set format routine */
cstate->routine = CopyFromGetRoutine(cstate->opts);
if (!cstate->opts.binary)
    if (cstate->opts.csv_mode)
        cstate->copy_read_attributes = CopyReadAttributesCSV;
    else
        cstate->copy_read_attributes = CopyReadAttributesText;

Example2:

static void
CopyFromSetRoutine(CopyFromState cstate)
{
    if (cstate->opts.csv_mode)
    {
        cstate->routine = &CopyFromRoutineCSV;
        cstate->copy_read_attributes = CopyReadAttributesCSV;
    }
    else if (cstate.binary)
        cstate->routine = &CopyFromRoutineBinary;
    else
    {
        cstate->routine = &CopyFromRoutineText;
        cstate->copy_read_attributes = CopyReadAttributesText;
    }
}

BeginCopyFrom()
{
    /* Set format routine */
    CopyFromSetRoutine(cstate);
}


But I don't object your original approach. If we have the
extra callbacks in Copy{From,To}Routines, I just don't use
them for my custom format extension.

>> What is the better next action for us? Do you want to
>> complete the WIP v11 patch set by yourself (and commit it)?
>> Or should I take over it?
> 
> I was planning to work on that, but wanted to be sure how you felt
> about the problem with text and csv first.

OK.
My opinion is the above. I have an idea how to implement it
but it's not a strong idea. You can choose whichever you like.


Thanks,
-- 
kou