Date: Thu, 19 Mar 2020 16:56:46 -0400
From: Bruce Momjian <bruce@momjian.us>
To: splarv@ya.ru, pgsql-docs@lists.postgresql.org
Subject: Re: explanation for random_page_cost is outdated
Message-ID: <20200319205646.GB28431@momjian.us>
References: <158281492445.30439.15446208692175239579@wrigleys.postgresql.org>
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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 Explanation for random_page_cost is rather outdated, because it did only for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.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +