Re: explanation for random_page_cost is outdated

On Thu, Feb 27, 2020 at 02:48:44PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
>
> Page: https://www.postgresql.org/docs/12/runtime-config-query.html
> Description:
>
> Explanation for random_page_cost is rather outdated, because it did only for
> case of mechanical hdd. But all modern database servers, which I know, made
> upon SSD. Do or not do default value for random_page_cost equal to 1 is the
> question, but, IMHO, at list in the documentation about random_page_cost
> need to add in a speculation about SSD.
>
> It's important because a business programming now is mostly web programming.
> Most database is poorly designed by web programmer, tables looked like a
> primary key and a huge json (containing all) with large gin index upon it.
> Now I am seeing a table with a GIN index 50% of the table size. The database
> is on SSD, of cause. With default random_page_cost=4 GIN index don't used
> by planner, but with random_page_cost=1 the result may be not excellent, but
> acceptable for web programmers.

Does this sentence in the random_page_cost docs unclear or not have enough
visibility:

https://www.postgresql.org/docs/12/runtime-config-query.html#RUNTIME-CONFIG-QUERY-CONSTANTS

Storage that has a low random read cost relative to sequential, e.g.
solid-state drives, might also be better modeled with a lower value for
random_page_cost.

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Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

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