On 2014-05-07 13:32:41 -0500, Merlin Moncure wrote: > On Wed, May 7, 2014 at 1:13 PM, Peter Geoghegan <p...@heroku.com> wrote: > > On Wed, May 7, 2014 at 11:04 AM, Josh Berkus <j...@agliodbs.com> wrote: > >> Unfortunately nobody has the time/resources to do the kind of testing > >> required for a new recommendation for shared_buffers. > > > > I meant to suggest that the buffer manager could be improved to the > > point that the old advice becomes obsolete. Right now, it's much > > harder to analyze shared_buffers than it should be, presumably because > > of the problems with the buffer manager. I think that if we could > > formulate better *actionable* advice around what we have right now, > > that would have already happened. > > > > We ought to be realistic about the fact that the current > > recommendations around sizing shared_buffers are nothing more than > > folk wisdom. That's the best we have right now, but that seems quite > > unsatisfactory to me. > > I think the stock advice is worse then nothing because it is A. based > on obsolete assumptions and B. doesn't indicate what the tradeoffs are > or what kinds of symptoms adjusting the setting could alleviate. The > documentation should be reduced to things that are known, for example: > > *) 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. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
