On Wed, May 7, 2014 at 11:38 AM, Andres Freund <and...@2ndquadrant.com>wrote:
> On 2014-05-07 13:32:41 -0500, Merlin Moncure wrote: > > > > *) raising shared buffers does not 'give more memory to postgres for > > caching' -- it can only reduce it via double paging > > That's absolutely not a necessary consequence. If pages are in s_b for a > while the OS will be perfectly happy to throw them away. > Is that an empirical observation? I've run some simulations a couple years ago, and also wrote some instrumentation to test that theory under favorably engineered (but still plausible) conditions, and couldn't get more than a small fraction of s_b to be so tightly bound in that the kernel could forget about them. Unless of course the entire workload or close to it fits in s_b. Cheers, Jeff
