Re: Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost

On Mon, 2024-03-11 at 12:30 +0000, PG Doc comments form wrote:
> While reading the following section in the documentation
> https://www.postgresql.org/docs/current/runtime-config-query.html#GUC-RANDOM-PAGE-COST
> I found something which looks incorrect to me.
>
> If I understand this setting correctly, the following sentence:
>
> "Reducing this value relative to seq_page_cost will cause the system to
> prefer index scans; raising it will make index scans look relatively more
> expensive."
>
> should rather be:
>
> "Raising this value relative to seq_page_cost will cause the system to
> prefer index scans; reducing it will make index scans look relatively more
> expensive."

The documentation is correct.  If the cost of a random I/O operation is
higher, index scans look more expensive, because they perform random I/O.

Yours,
Laurenz Albe