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Date: Thu, 24 Apr 2025 10:02:10 +0200
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Subject: Re: Another documentation issue
To: Daniel Gustafsson <daniel@yesql.se>,
 Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Igor Korot <ikorot01@gmail.com>,
 "pgsql-generallists.postgresql.org" <pgsql-general@lists.postgresql.org>
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From: Peter Eisentraut <peter@eisentraut.org>
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On 23.04.25 11:14, Daniel Gustafsson wrote:
>> On 23 Apr 2025, at 09:16, Laurenz Albe <laurenz.albe@cybertec.at> wrote:
>> On Wed, 2025-04-23 at 00:21 -0500, Igor Korot wrote:
> 
>>> However, this page
>>> https://www.postgresql.org/docs/current/runtime-config-resource.html#GUC-EFFECTIVE-IO-CONCURRENCY
>>> describes both default and mn/max, however t s says:
>>>
>>> [quote]
>>> The default is 1 on supported systems, otherwise 0
>>> [/quote]]
>>>
>>> No explanation of what is "supported system" is given...
>>>
>>> And the same can be said about
>>> https://www.postgresql.org/docs/current/runtime-config-resource.html#GUC-MAINTENANCE-IO-CONCURRENCY.
>>
>> According to the source, it is "systems that have posix_fadvise()".  We could document that,
>> but I don't know if it would help many people.  I am not sure how easy and feasible it is
>> to research which versions of which operating systems qualify.
> 
>  From memory it's supported on FreeBSD, NetBSD and Linux with Windows, macOS and
> OpenBSD not supporting it.  Assuming I'm not completely wrong (a 1 minute
> search shows it's in the ballpark) we could perhaps add something like
> "Unsupported platforms include (but isn't limited to) Windows and macOS" which
> would provide a bit more clarity.

Note that PG18 supports prefetching on macOS without posix_fadvise(), 
and we changed some of the documentation text to not mention 
posix_fadvise() anymore.  Also, some of the text and the defaults have 
changed because of the async IO feature set.  Maybe see if the text in 
master provides the information you need.