explanation for random_page_cost is outdated

From: PG Doc comments form <noreply(at)postgresql(dot)org>
To: pgsql-docs(at)lists(dot)postgresql(dot)org
Cc: splarv(at)ya(dot)ru
Subject: explanation for random_page_cost is outdated
Date: 2020-02-27 14:48:44
Message-ID: 158281492445.30439.15446208692175239579@wrigleys.postgresql.org
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Page: https://www.postgresql.org/docs/12/runtime-config-query.html
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Explanation for random_page_cost is rather outdated, because it did only for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.

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