doc: rewrite random_page_cost description

Bruce Momjian <bruce@momjian.us>

Commit: 3f0b994cf3a68b74f63cd6f9bde954cc0ae70ceb
Author: Bruce Momjian <bruce@momjian.us>
Date: 2025-10-30T23:11:53Z
Releases: 17.7
doc:  rewrite random_page_cost description

This removes some of the specifics of how the default was set, and adds
a mention of latency as a reason the value is lower than the storage
hardware might suggest.  It still mentions caching.

Discussion: https://postgr.es/m/CAKAnmmK_nSPYr53LobUwQD59a-8U9GEC3XGJ43oaTYJq5nAOkw@mail.gmail.com

Backpatch-through: 13

Files

PathChange+/−
doc/src/sgml/config.sgml modified +18 −18

Documentation touched