From: Олег Самойлов <splarv@ya.ru>
To: Bruce Momjian <bruce@momjian.us>
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: explanation for random_page_cost is outdated
Date: Fri, 24 Apr 2020 03:47:13 +0300
Message-ID: <72492300-BFD4-4CCF-9136-20CC41A18A10@ya.ru> (raw)
In-Reply-To: <20200319205646.GB28431@momjian.us>
References: <20200319205646.GB28431@momjian.us>
Yep. Unclear. What parameter is recommended for SSD? Lower? 3? 2? 1?
Much better will be write: if you use SSD set 1.
Олег
> 19 марта 2020 г., в 23:56, Bruce Momjian <bruce@momjian.us> 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 Explanation for random_page_cost is rather outdated, because it did only for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 <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 +
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To: pgsql-docs@postgresql.org
Cc: splarv@ya.ru, bruce@momjian.us, pgsql-docs@lists.postgresql.org
Subject: Re: explanation for random_page_cost is outdated
In-Reply-To: <72492300-BFD4-4CCF-9136-20CC41A18A10@ya.ru>
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