Re: [GENERAL] ShmemAlloc maximum size

On Thu, Feb 23, 2017 at 08:17:54PM +0530, hari.prasath wrote:
> I am trying to get some 15MB of shared memory using ShmemAlloc.
>
> Cross checked all my kernal variables set in OS level and also in postgresql.conf.
>
> Cant able to get the required memory(15MB) but if i try with some small memory(1MB), its working fine.
>
> Am i missing something.?

Assuming you're talking about some C extension, you have to request in
_PG_INIT() the amount of shmem you'll need, with RequestAddinShmemSpace().

You can see an example in pg_stat_statements.c how it's done (_PG_INIT() and
pgss_shmem_startup()).

Asking a small amount probably works because some shared memory is requested
but not totally used as soon as the server starts.

Regards.

--
Julien Rouhaud
http://dalibo.com - http://dalibo.org