| From: | Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com>, Alena Rybakina <a(dot)rybakina(at)postgrespro(dot)ru> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Peter Geoghegan <pg(at)bowt(dot)ie>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: On disable_cost |
| Date: | 2024-10-03 04:31:50 |
| Message-ID: | 0ca6e59ab4f44474ddabde10d9a43af6f3f7a31d.camel@cybertec.at |
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| Lists: | pgsql-hackers |
On Thu, 2024-10-03 at 11:44 +1300, David Rowley wrote:
> 2) Laurenz is misunderstanding what "Disabled Nodes" means. It has
> nothing to do with other Paths which were considered and rejected. It
> might be better named as "Disabled Degree". It tracks how many plan
> nodes below and including this node are disabled.
>
> Because of #2, I think I now understand why Laurenz was interested in
> only showing this with VERBOSE. If it worked the way Laurenz thought,
> I'd probably agree with him.
Ah, thanks, now I see the light.
You only see a "disabled node" if the optimizer chose a node you explicitly
disabled, like a sequential scan, a nested loop join or a sort.
I completely agree with you: it should always be displayed, and a boolean is
the appropriate way. The display just shouldn't be propagated up the tree
to nodes that were not actually disabled.
Perhaps a line of documentation on the EXPLAIN reference page or on the
"Using EXPLAIN" page would be in order.
Yours,
Laurenz Albe
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