Horton

Re: psql's FETCH_COUNT (cursor) is not being respected for CTEs

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Daniel Verite <daniel@manitou-mail.org>, Jakub Wartak <jakub.wartak@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2023-01-04T17:38:17Z
Lists: pgsql-hackers 
On Wed, Jan 4, 2023 at 11:36 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 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.

Yeah, I was vaguely worried that there might be more per-row overhead,
not that I know a lot about this topic. I wonder if there's a way to
mitigate that. I'm a bit suspicious that what we want here is really
more of an incremental mode than a single-row mode i.e. yeah, you want
to fetch rows without materializing the whole result, but maybe not in
batches of exactly size one.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

  1. Further review for re-implementation of psql's FETCH_COUNT feature.

  2. Re-implement psql's FETCH_COUNT feature atop libpq's chunked mode.

  3. Support retrieval of results in chunks with libpq.

  4. Attempt to fix newly added Memoize regression test