Re: Is there a significant difference in Memory settings between 9.5 and 12

On Mon, May 11, 2020 at 1:36 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Tory M Blue <tmblue(at)gmail(dot)com> writes:
> > 12 will not start at 10GB, even though it's the same hardware, same
> config
> > file, same physical box, same everything, just version 12 vs 9.5
>
> For me, using all-default settings (in particular, shared_buffers =
> 128MB), the shared memory block is about 141.6MB using 9.5 and 142.1MB
> using 12. So there's half a meg or so of additional data in v12, but
> certainly not gigabytes worth.
>
> Are you trying to start both postmasters concurrently? Maybe you're
> hitting some kernel limit on the total amount of shared memory in the
> system.
>
> regards, tom lane
>

Hey Tom

Nope, just a single one that is why i'm flummoxed :) I've even rebooted,
but I can't start Postgres 12 with my current setting of 10GB, I can start
9.5 with 10GB configured. I've tried, shutting down 9.5 and rebooting so
nothing is running and attempting to start 12 and nada, it won't unless I
drop the Shared Buffers down to 5GB (half).. But these are dedicated
postgresql servers. And in fact my latest migrations, don't even have 9.5
binaries anymore and 12 will not start with my 9.5 configuration of 10GB
buffers. So something feels really different.

It's very possible that there are new defaults , new memory settings that
I'm not finding in the default postgresql 12 .conf file, and my include is
not overwriting it. But really I just can't fathom what that could be..
Buffers, work mem, effective cache, what would they have added?

I am going to pull the settings from postgres itself and compare 12 and 9.5
to see if there is something glaring.

Thanks! :)
Tory