Re: explanation for random_page_cost is outdated

Yep. Unclear. What parameter is recommended for SSD? Lower? 3? 2? 1?

Much better will be write: if you use SSD set 1.

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> 19 марта 2020 г., в 23:56, Bruce Momjian  написал(а):
> 
> 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 Explanation for random_page_cost is rather outdated, because it did only for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          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 +