Date: Tue, 8 Feb 2022 12:00:41 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Fabien COELHO <coelho@cri.ensmp.fr>,
	Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: libpq async duplicate error results
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On 2022-Feb-07, Tom Lane wrote:

> In any case, the particular example we're looking at here is connection
> loss, which is not something that should greatly concern us as far as
> pipeline semantics are concerned, because you're not getting any more
> pipelined results anyway if that happens.  In the non-I/O-error case,
> I see that PQgetResult does a hacky "resetPQExpBuffer(&conn->errorMessage)"
> in between pipelined queries.  It seems like if there are real usability
> issues in this area, they probably come from that not being well placed.
> In particular, I wonder why that's done with the pqPipelineProcessQueue
> call in the PGASYNC_IDLE stanza, yet not with the pqPipelineProcessQueue
> call in the PGASYNC_READY stanza (where we're returning a PIPELINE_SYNC
> result).  It kinda looks to me like maybe pqPipelineProcessQueue
> ought to have the responsibility for doing that, rather than having
> two out of the three call sites do it.  Also it would seem more natural
> to associate it with the reinitialization that happens inside
> pqPipelineProcessQueue.

Yeah, I agree that the placement of error message reset in pipelined
libpq is more ad-hoc to the testing I was doing than carefully
principled.  I didn't test changing it, but on a quick look your
proposed change seems reasonable to me.

-- 
Álvaro Herrera           39°49'30"S 73°17'W  —  https://www.EnterpriseDB.com/
"Pensar que el espectro que vemos es ilusorio no lo despoja de espanto,
sólo le suma el nuevo terror de la locura" (Perelandra, C.S. Lewis)