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From: Stijn Sanders <stijnsanders@gmail.com>
Date: Sun, 5 Jan 2025 22:11:16 +0100
Message-ID: <CAHYFsWWPQZj4J5=AE7b=zrY31Nkff-=D8O6=tXx-MiO83K6FJg@mail.gmail.com>
Subject: Will PQsetSingleRowMode get me results faster?
To: pgsql-general@lists.postgresql.org
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I've been using LibPQ to get data from PostgreSQL instances with great
success.
I'm using PQsendQuery and PQgetResult, but noticed there's
also PQsetSingleRowMode.
The documentation is clearly stating it only benefits a limited set of
scenario's, but I'm saddened that it can't help to get the first resulte of
a (longer running) query faster.

There's a different database solution I won't name here that has a thing
they call 'firehose mode' that in fact does this: their equivalent
of PQntuples actually returns -1 in this mode, and you're expected to use
their equivalent of PQgetResult to get record per record ** as it is
rolling in from the server while the query is still running **.

From what I notice using LibPQ, it appears a query needs to complete before
resulting data is being transferred to the client. Please correct me if I'm
wrong.

Please point me in the correct direction if I'm missing something and I
need to look elsewhere. (I just now notice there's a PQsetChunkedRowsMode
now =E2=80=94nice! =E2=80=94 but I suspect the above still holds.)

Should I attempt to use LIMIT and OFFSET to limit the running time of
queries to get results faster? This will still interrupt the query and add
overhead of starting and stopping each query, even using PQexecPrepared, I
guess...

Greetings
Stijn

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<div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:verdana,=
sans-serif;color:#660000">I&#39;ve been using LibPQ to get data from Postgr=
eSQL instances with great success.</div><div class=3D"gmail_default" style=
=3D"font-family:verdana,sans-serif;color:#660000">I&#39;m using=C2=A0PQsend=
Query and=C2=A0PQgetResult, but noticed there&#39;s also=C2=A0PQsetSingleRo=
wMode.</div><div class=3D"gmail_default" style=3D"font-family:verdana,sans-=
serif;color:#660000">The documentation is clearly stating it only benefits =
a limited set of scenario&#39;s, but I&#39;m saddened that it can&#39;t hel=
p to get the first resulte of a (longer running) query faster.</div><div cl=
ass=3D"gmail_default" style=3D"font-family:verdana,sans-serif;color:#660000=
"><br></div><div class=3D"gmail_default" style=3D"font-family:verdana,sans-=
serif;color:#660000">There&#39;s a different database solution I won&#39;t =
name here that has a thing they call &#39;firehose mode&#39; that in fact d=
oes this: their equivalent of=C2=A0PQntuples actually returns -1 in this mo=
de, and you&#39;re expected to use their equivalent of PQgetResult to get r=
ecord per record ** as it is rolling in from the server while the query is =
still running **.</div><div class=3D"gmail_default" style=3D"font-family:ve=
rdana,sans-serif;color:#660000"><br></div><div class=3D"gmail_default" styl=
e=3D"font-family:verdana,sans-serif;color:#660000">From what I notice using=
 LibPQ, it appears a query needs to complete before resulting data is being=
 transferred to the client. Please correct me if I&#39;m wrong.</div><div c=
lass=3D"gmail_default" style=3D"font-family:verdana,sans-serif;color:#66000=
0"><br></div><div class=3D"gmail_default" style=3D"font-family:verdana,sans=
-serif;color:#660000">Please point me in the correct direction if I&#39;m m=
issing something and I need to look elsewhere. (I just now notice there&#39=
;s a=C2=A0PQsetChunkedRowsMode now =E2=80=94nice! =E2=80=94 but I suspect t=
he above still holds.)</div><div class=3D"gmail_default" style=3D"font-fami=
ly:verdana,sans-serif;color:#660000"><br></div><div class=3D"gmail_default"=
 style=3D"font-family:verdana,sans-serif;color:#660000">Should I attempt to=
 use LIMIT and OFFSET to limit the running time of queries to get results f=
aster? This will still interrupt the query and add overhead of starting and=
 stopping each query, even using=C2=A0PQexecPrepared, I guess...</div><div =
class=3D"gmail_default" style=3D"font-family:verdana,sans-serif;color:#6600=
00"><br></div><div class=3D"gmail_default" style=3D"font-family:verdana,san=
s-serif;color:#660000">Greetings</div><div class=3D"gmail_default" style=3D=
"font-family:verdana,sans-serif;color:#660000">Stijn</div></div>

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