From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jeff Janes <jeff.janes@gmail.com>
cc: Jerry Brenner <jbrenner@guidewire.com>,
        pgsql-performance@lists.postgresql.org
Subject: Re: Questions about "Output" in EXPLAIN ANALYZE VERBOSE
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Comments: In-reply-to Jeff Janes <jeff.janes@gmail.com>
	message dated "Tue, 02 Jan 2024 14:15:52 -0500"
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Date: Tue, 02 Jan 2024 14:23:36 -0500
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Jeff Janes <jeff.janes@gmail.com> writes:
> On Tue, Jan 2, 2024 at 1:29=E2=80=AFPM Jerry Brenner <jbrenner@guidewire=
.com> wrote:
>> - It looks like "Output" includes more than just the columns with
>> predicates and/or being accessed or returned in other nodes.

> Not in my hands. For SELECTs it just lists the columns that are needed.

It depends.  The planner may choose to tell a non-top-level scan node
to return all columns, in hopes of saving a tuple projection step at
runtime.  That's heuristic and depends on a number of factors, so you
shouldn't count on it happening or not happening.

			regards, tom lane