Re: POC PATCH: copy from ... exceptions to: (was Re: VLDB Features)

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Damir Belyalov <dam(dot)bel07(at)gmail(dot)com>
Cc: Danil Anisimow <anisimow(dot)d(at)gmail(dot)com>, "HukuToc(at)gmail(dot)com" <HukuToc(at)gmail(dot)com>, torikoshia <torikoshia(at)oss(dot)nttdata(dot)com>, "a(dot)lepikhov(at)postgrespro(dot)ru" <a(dot)lepikhov(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: POC PATCH: copy from ... exceptions to: (was Re: VLDB Features)
Date: 2023-02-06 05:52:33
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On February 5, 2023 9:12:17 PM PST, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>Damir Belyalov <dam(dot)bel07(at)gmail(dot)com> writes:
>>> I don't think this is the right approach. Creating a subtransaction for
>>> each row will cause substantial performance issues.
>> Subtransactions aren't created for each row. The block of rows in one
>> subtransaction is 1000 (SAFE_BUFFER_SIZE) and can be changed.
>I think that at this point, any patch that involves adding subtransactions
>to COPY is dead on arrival; whether it's batched or not is irrelevant.
>(It's not like batching has no downsides.)


>> InputFunctionCallSafe() is good for detecting errors from input-functions
>> but there are such errors from NextCopyFrom () that can not be detected
>> with InputFunctionCallSafe(), e.g. "wrong number of columns in row''.
>If you want to deal with those, then there's more work to be done to make
>those bits non-error-throwing. But there's a very finite amount of code
>involved and no obvious reason why it couldn't be done. The major problem
>here has always been the indefinite amount of code implicated by calling
>datatype input functions, and we have now created a plausible answer to
>that problem.

I'm not even sure it makes sense to avoid that kind of error. And invalid column count or such is something quite different than failing some data type input routine, or falling a constraint.

Sent from my Android device with K-9 Mail. Please excuse my brevity.

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