Re: Kernel settings shmall

On Thu, Sep 7, 2023, at 6:02 PM, PG Doc comments form wrote:
> The kernel parameter shmall is only in pages in Linux but your documentation
> says it can also be in bytes. Maybe it's in bytes with some OS other than
> Linux but the way it is presented in table 18.1 is quite misleading.. Could
> you add "depending on the OS" or something similar ? Many colleagues using
> Linux think it can be in bytes with Linux. Could you rewrite that part ?
> Table 18.1 in chapter 18.4.1
>

The information is accurate. It says

same as SHMMAX *if* bytes, or ceil(SHMMAX/PAGE_SIZE) *if* pages

and the Linux documentation [1] says its unit is *pages*.

You can claim that you always need to check if it is pages or bytes because you
don't remember. I'm not sure if changing the order would be better because most
of the supported operating systems use pages as unit. Is there any supported OS
that still uses bytes as unit? Linux, FreeBSD, OpenBSD and macOS use pages; I'm
not sure if any of the currently supported operating system [2] uses bytes. If
not, my suggestion is to remove the "bytes" part.

[1] https://www.kernel.org/doc/Documentation/sysctl/kernel.txt
[2] https://www.postgresql.org/docs/current/supported-platforms.html

--
Euler Taveira
EDB https://www.enterprisedb.com/