Craig James <cjames@xxxxxxxxxxxxxx> wrote: > On 11/21/2012 08:05 AM, Heikki Linnakangas wrote: > > Rather than telling the planner what to do or not to do, I'd much rather > > have hints that give the planner more information about the tables and > > quals involved in the query. A typical source of bad plans is when the > > planner gets its cost estimates wrong. So rather than telling the > > planner to use a nested loop join for "a INNER JOIN b ON a.id = b.id", > > the user could tell the planner that there are only 10 rows that match > > the "a.id = b.id" qual. That gives the planner the information it needs > > to choose the right plan on its own. That kind of hints would be much > > less implementation specific and much more likely to still be useful, or > > at least not outright counter-productive, in a future version with a > > smarter planner. > > > > You could also attach that kind of hints to tables and columns, which > > would be more portable and nicer than decorating all queries. > > I like this idea, but also think that if we have a syntax to allow > hints, it would be nice to have a simple way to ignore all hints (yes, I > suppose I'm suggesting yet another GUC). That way after sprinkling your > SQL with hints, you could easily periodically (e.g. after a Postgres > upgrade) test what would happen if the hints were removed. > > > Or a three-way choice: Allow, ignore, or generate an error. That would allow > developers to identify where hints are being used. > > Craig +1 I think, we HAVE a smart planner, but hints in this direction are okay, and we need a simple way to make such hints obsolete - for/in the future. Andreas -- Really, I'm not out to destroy Microsoft. That will just be a completely unintentional side effect. (Linus Torvalds) "If I was god, I would recompile penguin with --enable-fly." (unknown) Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889° -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
