Re: Shared memory usage in PostgreSQL 9.1

On 4.12.2011 15:06, Stephen Frost wrote:
> * Christoph Zwerschke (cito@online.de) wrote:
>> (Btw, what negative consequences - if any - does it have if I set
>> kernel.shmmax higher as necessary, like all available memory? Does
>> this limit serve only as a protection against greedy applications?)
>
> Didn't see this get answered...  The long-and-short of that there aren't
> any negative consequences of having it higher, as I understand it
> anyway, except the risk of greedy apps.  In some cases, shared memory
> can't be swapped out, which makes it a bit more risky than 'regular'
> memory getting sucked up by some app.

AFAIK it's "just" a protection. It simply allows more memory to be
allocated as shared segments. If you care about swapping, you should
tune vm.swappiness kernel parameter (and vm.overcommit is your friend too).

Tomas