Horton

Re: On disable_cost

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, David Rowley <dgrowleyml@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Peter Geoghegan <pg@bowt.ie>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-10-02T14:08:50Z
Lists: pgsql-hackers 
On Fri, Sep 27, 2024 at 4:42 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
> 1. The "disabled nodes" are always displayed.
>    I'd be happier if it were only shown for COSTS ON, but I think it
>    would be best if they were only shown with VERBOSE ON.
>
>    After all, the messages are pretty verbose...

I agree that the messages are more verbose than what we did before
(add a large value to the cost). But I would have thought it wouldn't
matter much because most of the time nothing will be disabled. And I
would think if you get a plan that has some nodes disabled, you would
want to know about that.

I actually thought it was rather nice that this system lets you show
the disabled-nodes information even when COSTS OFF. Regression tests
need to suppress costs because it can vary by platform, but the count
of disabled nodes is stable enough to display.

-- 
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.