Horton

Re: On disable_cost

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Alena Rybakina <a.rybakina@postgrespro.ru>, David Rowley <dgrowleyml@gmail.com>, Laurenz Albe <laurenz.albe@cybertec.at>, Tom Lane <tgl@sss.pgh.pa.us>, Heikki Linnakangas <hlinnaka@iki.fi>, Peter Geoghegan <pg@bowt.ie>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-10-07T15:28:15Z
Lists: pgsql-hackers 
On 2024-Oct-03, Robert Haas wrote:

> One general thing to think about is that we really document very
> little about EXPLAIN. That might not be good, but we should consider
> whether it will look strange if we document a bunch of stuff about
> this and still don't talk about anything else.

I completely agree that we document very little about EXPLAIN.  However,
I disagree that we should continue to do so.  I'd rather take the
opportunity to _add_ more details that we currently omit, and make the
documentation more complete.  A short blurb about Disabled Nodes such as
the one Laurenz proposed seems an excellent way to start; we can add
more later, as people propose them.  We don't have to stop here, and we
don't have to stay at statu quo re. other points.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
Officer Krupke, what are we to do?
Gee, officer Krupke, Krup you! (West Side Story, "Gee, Officer Krupke")

Commits

  1. Doc: add detail about EXPLAIN's "Disabled" property

  2. Adjust EXPLAIN's output for disabled nodes

  3. Fix order of parameters in a cost_sort call

  4. Show number of disabled nodes in EXPLAIN ANALYZE output.

  5. Treat number of disabled nodes in a path as a separate cost metric.

  6. Remove grotty use of disable_cost for TID scan plans.