Horton

Re: problems with "Shared Memory and Semaphores" section of docs

Sami Imseih <simseih@amazon.com>

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From: "Imseih (AWS), Sami" <simseih@amazon.com>
To: Nathan Bossart <nathandbossart@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Justin Pryzby <pryzby@telsasoft.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2024-05-17T18:30:08Z
Lists: pgsql-hackers 
>>> If the exact values
>>> are important, maybe we could introduce more GUCs like
>>> shared_memory_size_in_huge_pages that can be consulted (instead of
>>> requiring users to break out their calculators).
>>
>> I don't especially like shared_memory_size_in_huge_pages, and I don't
>> want to introduce more of those. GUCs are not the right way to expose
>> values that you can't actually set. (Yeah, I'm guilty of some of the
>> existing ones like that, but it's still not a good thing.) Maybe it's
>> time to introduce a system view for such things? It could be really
>> simple, with name and value, or we could try to steal some additional
>> ideas such as units from pg_settings.

I always found some of the preset GUCs [1] to be useful for writing SQLs used by
DBAs, particularly block_size, wal_block_size, server_version and server_version_num.

> The advantage of the GUC is that its value could be seen before trying to
> actually start the server. 

Only if they have a sample in postgresql.conf file, right? 
A GUC like shared_memory_size_in_huge_pages will not be.


[1] https://www.postgresql.org/docs/current/runtime-config-preset.html


Regards,

Sami

Commits

  1. Introduce num_os_semaphores GUC.

  2. Fix documentation for POSIX semaphores.

  3. Fix documentation for System V semaphores.