On Mon, Oct 19, 2009 at 5:08 PM, marcin mank <marcin.m...@gmail.com> wrote: > Currently random_page_cost is a GUC. I propose that this could be set > per-table. > > I think this is a good idea for widely-wanted planner hints. This way > You can say "I do NOT want this table to be index-scanned, because I > know it is not cached" by setting it`s random_page_cost to a large > value (an obviously You can do the other way around, when setting the > random_page_cost to 1 You say "I don`t care how You fetch the pages, > they are all in cache") > > The value for the per-table setting could be inferred from > pg_stat(io)?.*tables . We could have a tool to suggest appropriate > values. > > We could call it something like cached_percentage (and have the cost > of a random tuple fetch be inferred from the global random_page_cost, > seq_tuple_cost and the per-table cached_percentage). Then we could set > the global random_page_cost to a sane value like 200. Now one can > wonder why the planner works while having such blantantly unrealistic > values for random_page_cost :) > > What do You think?
I've been thinking about this a bit, too. I've been wondering if it might make sense to have a "random_page_cost" and "seq_page_cost" setting for each TABLESPACE, to compensate for the fact that different media might be faster or slower, and a percent-cached setting for each table over top of that. ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
