From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Daniel Verite <daniel@manitou-mail.org>,
        Jakub Wartak <jakub.wartak@enterprisedb.com>,
        PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: psql's FETCH_COUNT (cursor) is not being respected for CTEs
In-reply-to: 
 <CA+TgmoY+dtzL-AxgdjaZ7HS=AXr1Sd6w-ZCg9uCjW9dvoDZPrQ@mail.gmail.com>
References: 
 <CAKZiRmxsVTkO928CM+-ADvsMyePmU3L9DQCa9NwqjvLPcEe5QA@mail.gmail.com>
 <3a3451a2-7d05-4dd7-b7ac-e75d2accf327@manitou-mail.org>
 <CA+TgmoY+dtzL-AxgdjaZ7HS=AXr1Sd6w-ZCg9uCjW9dvoDZPrQ@mail.gmail.com>
Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Wed, 04 Jan 2023 10:57:28 -0500"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <2097212.1672850211.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Wed, 04 Jan 2023 11:36:51 -0500
Message-ID: <2097213.1672850211@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/2097213.1672850211%40sss.pgh.pa.us>
Precedence: bulk

Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Jan 4, 2023 at 10:22 AM Daniel Verite <daniel@manitou-mail.org> =
wrote:
>> A solution would be for psql to use PQsetSingleRowMode() to retrieve
>> results row-by-row, as opposed to using a cursor, and then allocate
>> memory for only FETCH_COUNT rows at a time.

> Is there any reason that someone hasn't, like, already done this?

As you well know, psql's FETCH_COUNT mechanism is far older than
single-row mode.  I don't think anyone's tried to transpose it
onto that.  I agree that it seems like a good idea to try.
There will be more per-row overhead, but the increase in flexibility
is likely to justify that.

			regards, tom lane