Hi, > -----Original Message----- > From: Robert Haas [mailto:robertmh...@gmail.com] > Sent: Wednesday, June 27, 2012 5:09 AM > To: Etsuro Fujita > Cc: Ants Aasma; Jay Levitt; Tom Lane; PostgreSQL-development; Francois Deliege > Subject: Re: [HACKERS] [PATCH] Lazy hashaggregate when no aggregation is needed > > On Fri, Jun 22, 2012 at 10:12 AM, Robert Haas <robertmh...@gmail.com> wrote: > > On Tue, Jun 19, 2012 at 5:41 AM, Etsuro Fujita > > <fujita.ets...@lab.ntt.co.jp> wrote: > >>> I'm confused by this remark, because surely the query planner does it this > >>> way only if there's no LIMIT. When there is a LIMIT, we choose based on > >>> the startup cost plus the estimated fraction of the total cost we expect > >>> to pay based on dividing the LIMIT by the overall row count estimate. Or > >>> is this not what you're talking about? > >> > >> I think that Ants is pointing the way of estimating costs in > >> choose_hashed_grouping()/choose_hashed_distinct(), ie cost_agg() for > >> cheapest_path + hashagg, where the costs are calculated based on the total > >> cost only of cheapest_path. I think that it might be good to do cost_agg() > >> for the discussed case with the AGG_SORTED strategy, not the AGG_HASHED > >> strategy. > > > > Well, Ants already made some adjustments to those functions; not sure > > if this means they need some more adjustment, but I don't see that > > there's a general problem with the costing algorithm around LIMIT. > > Ants, do you intend to update this patch for this CommitFest? Or at > all? It seems nobody's too excited about this, so I'm not sure > whether it makes sense for you to put more work on it. But please > advise as to your plans.
Please excuse my slow response, I would also like to know your plan. Best regards, Etsuro Fujita > Thanks, > > -- > Robert Haas > EnterpriseDB: http://www.enterprisedb.com > The Enterprise PostgreSQL Company > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers