Re: PATCH: Batch/pipelining support for libpq

From: "Daniel Verite" <daniel(at)manitou-mail(dot)org>
To: "Vaishnavi Prabakaran" <vaishnaviprabakaran(at)gmail(dot)com>
Cc: "Michael Paquier" <michael(dot)paquier(at)gmail(dot)com>,"Prabakaran, Vaishnavi" <VaishnaviP(at)fast(dot)au(dot)fujitsu(dot)com>,"Craig Ringer" <craig(at)2ndquadrant(dot)com>,"Haribabu Kommi" <kommi(dot)haribabu(at)gmail(dot)com>,"Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>,"Dmitry Igrishin" <dmitigr(at)gmail(dot)com>,"Andres Freund" <andres(at)anarazel(dot)de>,"PostgreSQL Hackers" <pgsql-hackers(at)postgresql(dot)org>,"Manuel Kniep" <m(dot)kniep(at)web(dot)de>,"fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp" <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>,"Iwata, Aya" <iwata(dot)aya(at)jp(dot)fujitsu(dot)com>
Subject: Re: PATCH: Batch/pipelining support for libpq
Date: 2017-03-13 17:19:39
Message-ID: a7123b26-f8b0-4252-bbd1-305cb1500e1d@manitou-mail.org
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Vaishnavi Prabakaran wrote:

> > while (QbatchQueueProcess(conn)) {
> > r = PQsetSingleRowMode(conn);
> > if (r!=1) {
> > fprintf(stderr, "PQsetSingleRowMode() failed");
> > }
> > ..

> Thanks for investigating the problem, and could you kindly explain what
> "next iteration" you mean here? Because I don't see any problem in
> following sequence of calls - PQbatchQueueProcess(),PQsetSingleRowMode()
> , PQgetResult()

I mean the next iteration of the above while statement. Referring
to the doc, that would be the "next batch entry":

" To get the result of the first batch entry the client must call
PQbatchQueueProcess. It must then call PQgetResult and handle the
results until PQgetResult returns null (or would return null if
called). The result from the next batch entry may then be retrieved
using PQbatchQueueProcess and the cycle repeated"

Attached is a bare-bones testcase showing the problem.
As it is, it works, retrieving results for three "SELECT 1"
in the same batch. Now in order to use the single-row
fetch mode, consider adding this:

r = PQsetSingleRowMode(conn);
if (r!=1) {
fprintf(stderr, "PQsetSingleRowMode() failed for i=%d\n", i);
}

When inserted after the call to PQbatchQueueProcess,
which is what I understand you're saying works for you,
it fails for me when starting to get the results of the 2nd query
and after.

Best regards,
--
Daniel Vérité
PostgreSQL-powered mailer: http://www.manitou-mail.org
Twitter: @DanielVerite

Attachment Content-Type Size
test-singlerow-batch.c application/octet-stream 981 bytes

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