Re: BUG #4575: All page cache in shared_buffers pinned (duplicated by OS, always)

On Thu, Dec 11, 2008 at 5:37 AM, Scott Carey <scott@richrelevance.com> wrote:
>
>
> Run top, and note the largest value of the "SHR" column on all postgres
> processes.  Now execute the os cache eviction.  Check the remaining cached
> memory.
> Note that it is now larger than the baseline by essentially the exact size
> of the postgres shared memory.
>

Isn't the shared memory on Linux non-swappable, unlike Solaris where
you have an option to make is swappable ? As and when shared memory
pages are accessed, they are allocated and can not be swapped out. I
don't know if these pages are counted as part of the OS cache, but
assuming they are, I don't see any problem with the above observation.

May be you can try to write a C program which creates, attaches and
accesses every page of the shared memory and check if you see the same
behavior.

Thanks,
Pavan

--
Pavan Deolasee
EnterpriseDB     http://www.enterprisedb.com