Tom Lane wrote: > Robert Haas <robertmhaas@xxxxxxxxx> writes: > > On Fri, Nov 12, 2010 at 4:15 AM, Cédric Villemain > > <cedric.villemain.debian@xxxxxxxxx> wrote: > >>> I wondering if we could do something with a formula like 3 * > >>> amount_of_data_to_read / (3 * amount_of_data_to_read + > >>> effective_cache_size) = percentage NOT cached. That is, if we're > >>> reading an amount of data equal to effective_cache_size, we assume 25% > >>> caching, and plot a smooth curve through that point. In the examples > >>> above, we would assume that a 150MB read is 87% cached, a 1GB read is > >>> 50% cached, and a 3GB read is 25% cached. > > >> But isn't it already the behavior of effective_cache_size usage ? > > > No. > > I think his point is that we already have a proven formula > (Mackert-Lohmann) and shouldn't be inventing a new one out of thin air. > The problem is to figure out what numbers to apply the M-L formula to. > > I've been thinking that we ought to try to use it in the context of the > query as a whole rather than for individual table scans; the current > usage already has some of that flavor but we haven't taken it to the > logical conclusion. Is there a TODO here? -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
