On Tue, Oct 20, 2009 at 1:21 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > If the parameter is defined as "the chance that a page is in cache" >> there is very real physical meaning to it. > > We have no such parameter...
What a simple person like me would think would work is: - call the parameter "cached_probability". - Invent a way to store it (I`d actually try to do it the exact same way recent "alter table set statistics distinct" does it) a) less radical idea: replace all usage of random_page_cost with seq_page_cost * cached_probability + random_page_cost * (1-cached_probability) b) more radical idea: b1) invent a new GUC: cached_page_cost b2) replace all usage of seq_page_cost with cached_page_cost * cached_probability + seq_page_cost * (1-cached_probability) b3) replace all usage of random_page_cost with cached_page_cost * cached_probability + random_page_cost * (1-cached_probability) > How would you come up with sensible figures for this hypothetical parameter? select schemaname,relname,heap_blks_hit / cast(heap_blks_read+heap_blks_hit+1 as float) from pg_statio_all_tables Would be a nice starting point. Greetings Marcin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
