| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Peter Geoghegan <pg(at)bowt(dot)ie>, David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: On disable_cost |
| Date: | 2024-07-02 17:54:02 |
| Message-ID: | CA+TgmoaX3DS0uDMZh+U7qi6BnFGJ2pC8TLXDrVkYf=-3cq2vbQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jul 2, 2024 at 1:40 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> FWIW, I disagree completely. I think it's entirely natural to
> consider bitmap index scans to be a subset of index scans, so that
> enable_indexscan should affect both. I admit that the current set
> of GUCs doesn't let you force a bitmap scan over a plain one, but
> I can't recall many people complaining about that. I don't follow
> the argument that this definition is somehow unmaintainable, either.
Well... but that's not what the GUC does either. Not now, and not with
the patch.
What happens right now is:
- If you set enable_indexscan=false, then disable_cost is added to the
cost of index scan paths and the cost of index-only scan paths.
- If you set enable_indexonlyscan=false, then index-only scan paths
are not generated at all.
Bitmap scans are controlled by enable_bitmapscan.
--
Robert Haas
EDB: http://www.enterprisedb.com
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