Horton

Re: On disable_cost

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Alena Rybakina <a.rybakina@postgrespro.ru>
Cc: 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: 2024-10-03T18:24:01Z
Lists: pgsql-hackers 
On Thu, Oct 3, 2024 at 1:35 PM Alena Rybakina <a.rybakina@postgrespro.ru> wrote:
> I think you are right, most users will perceive this parameter as the number of rejected paths, and not in any other way.
>
> To be honest, I don't have much experience writing documentation, but I think we should add a little more information to doc/src/sgml/perform.sgml.
>
> It contains a description about "explain queries", so the description of "Disabled nodes" is available there.
>
> I prepared a patch that includes the information we can add.

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.

(This is not a comment on this specific patch, which I have not
examined. It's just a general thought.)

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

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.