Feedback-ID: ia2694551:Fastmail
Date: Mon, 4 Dec 2023 19:47:51 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Ivan Trofimov <i.trofimow@yandex.ru>
Cc: "pgsql-bugs@lists.postgresql.org" <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #17948: libpq seems to misbehave in a pipelining corner case
Message-ID: <202312041847.iur3zphjejur@alvherre.pgsql>
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On 2023-Dec-02, Ivan Trofimov wrote:

> Thank you for looking into this, much appreciated.
> 
> Yes, I can confirm that the patch fixes both the busy-loop and
> client<->server desynchronization problem for me.

Great, thanks for the confirmation.

Mulling it over while writing better comments for it, I realized that it
could still be somewhat brittle, and it's also confusing that part of
the logic is in PQgetResult and the rest in pqCommandQueueAdvance; so I
moved it all to the latter, which also lets me document it more clearly
in the comments.  I addressed the brittleness by changing what to test:
instead of just "it's an error, then do nothing if the queue has a
SYNC", we can verify that we actually have a matching SYNC in both
places.  This seems much better.

Patch v2 attached.  I'll be pushing this to 14+ tomorrow, unless
something ugly comes up.

Thanks for reporting this problem!

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"El hombre nunca sabe de lo que es capaz hasta que lo intenta" (C. Dickens)

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