The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/15/runtime-config-query.html Description:
Two comments on random-page-cost parameter here https://www.postgresql.org/docs/current/runtime-config-query.html#GUC-RANDOM-PAGE-COST 1) Adding a paragraph reminding us what random-access really mean in postgres would be extremely valuable. I find the first paragraph from the index - only scan section perfect. "This means that in an ordinary index scan, each row retrieval requires fetching data from both the index and the heap. Furthermore, while the index entries that match a given indexable WHERE condition are usually close together in the index, the table rows they reference might be anywhere in the heap. The heap-access portion of an index scan thus involves a lot of random access into the heap, which can be slow, particularly on traditional rotating media. " 2) A question, based on the definition of what random-access mean in postgres (hits to the heap) does the random-page-cost affect index-only and covering index scans at all? (assume zero heap fetches from hints etc.)? if no can we also add a note there. thank you! Hussein