From: | "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com> |
---|---|
To: | "Scott Carey" <scott(at)richrelevance(dot)com> |
Cc: | pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: BUG #4575: All page cache in shared_buffers pinned (duplicated by OS, always) |
Date: | 2008-12-11 08:35:37 |
Message-ID: | 2e78013d0812110035q3a4378d5n6eed43c63817c2d8@mail.gmail.com |
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Lists: | pgsql-bugs |
On Thu, Dec 11, 2008 at 5:37 AM, Scott Carey <scott(at)richrelevance(dot)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
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