Le lundi 19 octobre 2009 23:14:40, Robert Haas a écrit : > 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.
At least settings by TABLESPACE should exists. I totaly agree with that. > > ...Robert > -- Cédric Villemain Administrateur de Base de Données Cel: +33 (0)6 74 15 56 53 http://dalibo.com - http://dalibo.org
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