doc: rewrite random_page_cost description

Bruce Momjian <bruce@momjian.us>

Commit: 6b4b8d5f359b24ccfa16093ed7051d5034fd1344
Author: Bruce Momjian <bruce@momjian.us>
Date: 2025-10-30T23:11:52Z
Releases: 13.23
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

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

Documentation touched