From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Support retrieval of results in chunks with libpq.
Date: Sun, 07 Apr 2024 00:45:33 +0000
Message-ID: <E1rtGf6-000t9x-SA@gemulon.postgresql.org> (raw)
Support retrieval of results in chunks with libpq.
This patch generalizes libpq's existing single-row mode to allow
individual partial-result PGresults to contain up to N rows, rather
than always one row. This reduces malloc overhead compared to plain
single-row mode, and it is very useful for psql's FETCH_COUNT feature,
since otherwise we'd have to add code (and cycles) to either merge
single-row PGresults into a bigger one or teach psql's
results-printing logic to accept arrays of PGresults.
To avoid API breakage, PQsetSingleRowMode() remains the same, and we
add a new function PQsetChunkedRowsMode() to invoke the more general
case. Also, PGresults obtained the old way continue to carry the
PGRES_SINGLE_TUPLE status code, while if PQsetChunkedRowsMode() is
used then their status code is PGRES_TUPLES_CHUNK. The underlying
logic is the same either way, though.
Daniel Vérité, reviewed by Laurenz Albe and myself (and whacked
around a bit by me, so any remaining bugs are my fault)
Discussion: https://postgr.es/m/CAKZiRmxsVTkO928CM+-ADvsMyePmU3L9DQCa9NwqjvLPcEe5QA@mail.gmail.com
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/4643a2b265e967cc5f13ffa0c7c6912dbb3466d0
Modified Files
--------------
doc/src/sgml/libpq.sgml | 107 +++++++++++----
.../libpqwalreceiver/libpqwalreceiver.c | 3 +-
src/bin/pg_amcheck/pg_amcheck.c | 1 +
src/interfaces/libpq/exports.txt | 1 +
src/interfaces/libpq/fe-exec.c | 146 +++++++++++++--------
src/interfaces/libpq/fe-protocol3.c | 3 +-
src/interfaces/libpq/libpq-fe.h | 4 +-
src/interfaces/libpq/libpq-int.h | 10 +-
src/test/modules/libpq_pipeline/libpq_pipeline.c | 40 ++++++
.../modules/libpq_pipeline/traces/singlerow.trace | 14 ++
10 files changed, 243 insertions(+), 86 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Support retrieval of results in chunks with libpq.
In-Reply-To: <E1rtGf6-000t9x-SA@gemulon.postgresql.org>
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