From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: Jerry Brenner <jbrenner@guidewire.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Questions about "Output" in EXPLAIN ANALYZE VERBOSE
Date: Tue, 02 Jan 2024 14:23:36 -0500
Message-ID: <4115743.1704223416@sss.pgh.pa.us> (raw)
In-Reply-To: <CAMkU=1ye8VMnyVjHND4DnsS0J+Nyjumg4HYGiK-TrB6XUtww=A@mail.gmail.com>
References: <CACoKFYSKJB3t-=8QLtaL1TvSOgu_XXHtk_mBMPpJu5Me7otQrA@mail.gmail.com>
<CAMkU=1ye8VMnyVjHND4DnsS0J+Nyjumg4HYGiK-TrB6XUtww=A@mail.gmail.com>
Jeff Janes <jeff.janes@gmail.com> writes:
> On Tue, Jan 2, 2024 at 1:29 PM 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
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, jeff.janes@gmail.com, jbrenner@guidewire.com, pgsql-performance@lists.postgresql.org
Subject: Re: Questions about "Output" in EXPLAIN ANALYZE VERBOSE
In-Reply-To: <4115743.1704223416@sss.pgh.pa.us>
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