From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Damir <dam.bel07@gmail.com>, torikoshia <torikoshia@oss.nttdata.com>,
        Pgsql Hackers <pgsql-hackers@postgresql.org>, daniel@yesql.se,
        anisimow.d@gmail.com, HukuToc@gmail.com,
        Andrey Lepikhov <a.lepikhov@postgrespro.ru>,
        Alena Rybakina <lena.ribackina@yandex.ru>
Subject: Re: POC PATCH: copy from ... exceptions to: (was Re: VLDB Features)
In-reply-to: <20231108235358.jmay4ps767mecrnu@awork3.anarazel.de>
References: <CALH1LguOY-VvJBWvjpLR2W3t0Z2p=LGSK5tzLrKwtzZ2UsqwGg@mail.gmail.com> <43399b33fe573f0548410893f41f84b6@oss.nttdata.com> <CALH1LgseNT7mxpGzQsQwOJz_UwYBo6L-4vR9tmJqb-WNPkt6Bg@mail.gmail.com> <8de9d5e1-2f81-ee2e-ece4-b1a6ede1f285@yandex.ru> <b74c1c3e3cc1c5d7ad5fb527b27d2b60@oss.nttdata.com> <c0fb57b82b150953f26a5c7e340412e8@oss.nttdata.com> <CALH1Lgtg39crESw644KDH+ejBWuW3Vospe67F-ZWXNeBMEE=PA@mail.gmail.com> <58fa3b63e88ffd0a09273e38aec0661e@oss.nttdat! a.com> <a303c70a-ca58-fd8d-e5f5-00b941f24667@gmail.com> <739953.1699467519@sss.pgh.pa.us> <20231108235358.jmay4ps767mecrnu@awork3.anarazel.de>
Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Wed, 08 Nov 2023 15:53:58 -0800"
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Date: Wed, 08 Nov 2023 19:00:01 -0500
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Andres Freund <andres@anarazel.de> writes:
> On 2023-11-08 13:18:39 -0500, Tom Lane wrote:
>> I think an actually usable feature of this sort would involve
>> copying all the failed lines to some alternate output medium,
>> perhaps a second table with a TEXT column to receive the original
>> data line.

> If we go in that direction, we should make it possible to *not* use such=
 a
> table as well, for some uses it'd be pointless.

Why?  You can always just drop the errors table if you don't want it.
But I fail to see the use-case for ignoring errors altogether.

> Another way of reporting errors could be for copy to return invalid inpu=
t back
> to the client, via the copy protocol.

Color me skeptical.  There are approximately zero clients in the
world today that could handle simultaneous return of data during
a COPY.  Certainly neither libpq nor psql are within hailing
distance of being able to support that.  Maybe in some far
future it could be made to work --- but if you want it in the v1
patch, you just moved the goalposts into the next county.

			regards, tom lane