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
>

Okay the one difference I see in settings is this little gem in 12..

shared_memory_type mmap

Otherwise i'm not seeing a ton of other settings not common between them,.

This is the only major difference I'm seeing, as it's really not an option
in 9.5..... Appears 9.5 was using

shared_memory_type (enum)

Specifies the shared memory implementation that the server should use for
the main shared memory region that holds PostgreSQL's shared buffers and
other shared data. Possible values are mmap (for anonymous shared memory
allocated using mmap), sysv (for System V shared memory allocated via shmget)
and windows (for Windows shared memory). Not all values are supported on
all platforms; the first supported option is the default for that platform.
The use of the sysv option, which is not the default on any platform, is
generally discouraged because it typically requires non-default kernel
settings to allow for large allocations (see Section 18.4.1
<https://www.postgresql.org/docs/12/kernel-resources.html#SYSVIPC>).