Merlin Moncure <mmoncure@gmail.com> wrote:
> On Wed, Jul 30, 2014 at 12:51 PM, Kevin Goess <kgoess@bepress.com> wrote:
>
>> A couple months ago we upgraded the RAM on our database servers from 48GB to
>> 64GB. Immediately afterwards the new RAM was being used for page cache,
>> which is what we want, but that seems to have dropped off over time, and
>> there's currently actually like 12GB of totally unused RAM.
> could be a numa issue.
I was thinking the same thing.
The other thought was that it could be a usage pattern and/or
monitoring issue. When there are transient requests for large
amounts of memory, it will discard cache to satisfy those (e.g.,
work_mem or maintenance_work_mem allocations). If the *active*
portion of the database is not as big as RAM, it might not refill
right away. This could be compounded on your monitoring graphs if
they summarize by taking the *average* RAM usage for an interval
rather than the *maximum* usage for that interval. Intermittent
spikes in usage could make it look like the RAM is unused if you
are averaging; personally, I would prefer to use maximum for a
metric like this. Many monitoring systems allow you to choose.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
