Re: 19c shared memory segments changes with AMM on Solaris

Pure speculation here, but it might be related to a little thread that started yesterday on twitter.
Some comments Tanel Poder made about the (new) MGA might be relevant: https://twitter.com/TanelPoder/status/1357021230625415169 Follow the whole thread to get the background - it's only 6 or 7 posts long at present.I'ev

I've pointed the thread back to your question on the Oracle-l server.

Regards
Jonathan Lewis

On Wed, 3 Feb 2021 at 17:11, Al B. <albert.y.balbekov_at_gmail.com> wrote:

> Hello listers,
>
> For those of you who are on Solaris - did you notice that 19c changed the
> way it allocates os shared memory segments when using AMM (MEMORY_TARGET) ?
> When checking with "pmap -xs" I am finding that it is not creating OSM
> (Optimized Shared Memory) segments.
> This was not happening in 12.1 and 12.2.
> Instead it creates numerous non-locked allocations in regular shared
> memory segments.
> Not OSM, not ISM and not DISM. Just regular shmid.
> Which of course makes them pageable and swappable and not a good thing.
> Even pmap -x runs noticeably slower.
>
> I also noticed that USE_LARGE_MEMORY value flips to False with AMM.
> This also was not happening in 12.1 and 12.2.
>
> According to the doc *"This parameter is applicable only on the Linux
> operating system. However, setting this parameter to FALSE can cause
> performance degradation on any platform"*
> Which makes me wonder - why does 19c flip it to false with AMM if it
> causes degradation ?
>
> I have SR where support confirmed that USE_LARGE_MEMORY flipping to false
> with AMM started in 19c.
> In SR they also stated that I should NOT try to set it back to true wen
> doing AMM (which I tested succeeds in making AMM use OSM segments again )
>
> Anybody knows of another way to make 19c use OSM Solaris segments with AMM
> ?
>
> Thank you
> Albert
>
>
>

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