EXPLAIN IndexOnlyScan shows disabled when enable_indexonlyscan=on

On Monday, October 21, 2024, David Rowley <dgrowleyml@gmail.com> wrote:

> On Tue, 22 Oct 2024 at 13:45, Melanie Plageman
> <melanieplageman@gmail.com> wrote:
> > I was surprised today when I saw that with
> > enable_indexscan=off
> > enable_indexonlyscan=on
>
> Robert did propose to change this behaviour while he was working on
> the disabled_nodes changes. I did push back on the proposed change
> [1]. If you feel strongly that what we have is wrong, then maybe it's
> worth opening the discussion about that again.
>

We should probably at least improve the documentation in 19.17.1; this
interaction is apparently not self-evident.

enable_indexscan

Enable or disable the planner’s use of both index-scan and index-only-scans
plan types.

enabled_indexonlyscan

Set to off to disable index-only-scan plan type while leaving index-scan
plan types enabled.  This setting has no effect if enable_indexscan is set
to off.

David J.