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* Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost
@ 2024-03-11 12:30 PG Doc comments form <noreply@postgresql.org>
2024-03-13 13:06 ` Re: Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost Laurenz Albe <laurenz.albe@cybertec.at>
0 siblings, 1 reply; 3+ messages in thread
From: PG Doc comments form @ 2024-03-11 12:30 UTC (permalink / raw)
To: pgsql-docs@lists.postgresql.org; +Cc: ignacio.alonso@microsoft.com
The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/16/runtime-config-query.html
Description:
While reading the following section in the documentation
https://www.postgresql.org/docs/current/runtime-config-query.html#GUC-RANDOM-PAGE-COST
I found something which looks incorrect to me.
If I understand this setting correctly, the following sentence:
"Reducing this value relative to seq_page_cost will cause the system to
prefer index scans; raising it will make index scans look relatively more
expensive."
should rather be:
"Raising this value relative to seq_page_cost will cause the system to
prefer index scans; reducing it will make index scans look relatively more
expensive."
Thanks,
Nacho
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost
2024-03-11 12:30 Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost PG Doc comments form <noreply@postgresql.org>
@ 2024-03-13 13:06 ` Laurenz Albe <laurenz.albe@cybertec.at>
2024-03-13 15:21 ` Re: [EXTERNAL] Re: Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost Nacho Alonso Portillo <Ignacio.Alonso@microsoft.com>
0 siblings, 1 reply; 3+ messages in thread
From: Laurenz Albe @ 2024-03-13 13:06 UTC (permalink / raw)
To: ignacio.alonso@microsoft.com; pgsql-docs@lists.postgresql.org
On Mon, 2024-03-11 at 12:30 +0000, PG Doc comments form wrote:
> While reading the following section in the documentation
> https://www.postgresql.org/docs/current/runtime-config-query.html#GUC-RANDOM-PAGE-COST
> I found something which looks incorrect to me.
>
> If I understand this setting correctly, the following sentence:
>
> "Reducing this value relative to seq_page_cost will cause the system to
> prefer index scans; raising it will make index scans look relatively more
> expensive."
>
> should rather be:
>
> "Raising this value relative to seq_page_cost will cause the system to
> prefer index scans; reducing it will make index scans look relatively more
> expensive."
The documentation is correct. If the cost of a random I/O operation is
higher, index scans look more expensive, because they perform random I/O.
Yours,
Laurenz Albe
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: [EXTERNAL] Re: Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost
2024-03-11 12:30 Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost PG Doc comments form <noreply@postgresql.org>
2024-03-13 13:06 ` Re: Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost Laurenz Albe <laurenz.albe@cybertec.at>
@ 2024-03-13 15:21 ` Nacho Alonso Portillo <Ignacio.Alonso@microsoft.com>
0 siblings, 0 replies; 3+ messages in thread
From: Nacho Alonso Portillo @ 2024-03-13 15:21 UTC (permalink / raw)
To: Laurenz Albe <laurenz.albe@cybertec.at>; pgsql-docs@lists.postgresql.org <pgsql-docs@lists.postgresql.org>
My bad. Misunderstood this when I read it. It's completely correct the way it is.
Thanks,
Nacho
________________________________
From: Laurenz Albe <laurenz.albe@cybertec.at>
Sent: Wednesday, March 13, 2024 2:06 PM
To: Nacho Alonso Portillo <Ignacio.Alonso@microsoft.com>; pgsql-docs@lists.postgresql.org <pgsql-docs@lists.postgresql.org>
Subject: [EXTERNAL] Re: Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost
[You don't often get email from laurenz.albe@cybertec.at. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
On Mon, 2024-03-11 at 12:30 +0000, PG Doc comments form wrote:
> While reading the following section in the documentation
> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.postgresql.org%2Fdocs%2Fcurren...;
> I found something which looks incorrect to me.
>
> If I understand this setting correctly, the following sentence:
>
> "Reducing this value relative to seq_page_cost will cause the system to
> prefer index scans; raising it will make index scans look relatively more
> expensive."
>
> should rather be:
>
> "Raising this value relative to seq_page_cost will cause the system to
> prefer index scans; reducing it will make index scans look relatively more
> expensive."
The documentation is correct. If the cost of a random I/O operation is
higher, index scans look more expensive, because they perform random I/O.
Yours,
Laurenz Albe
^ permalink raw reply [nested|flat] 3+ messages in thread
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2024-03-11 12:30 Definition of random_page_cost seems to invert correlation of that setting and seq_page_cost PG Doc comments form <noreply@postgresql.org>
2024-03-13 13:06 ` Laurenz Albe <laurenz.albe@cybertec.at>
2024-03-13 15:21 ` Nacho Alonso Portillo <Ignacio.Alonso@microsoft.com>
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