I've wordsmithed Chris's changes some, and then spun off a completely separate page for Hints discussion, since the NotToDo item was becoming too long. > Something like this syntax?: > > JOIN WITH (correlation_factor=0.3) Please, NO! This is exactly the kind of hint that I regard as a last resort if we run out of implementation alternatives. Any hint which gets coded into the actual queries becomes a *massive* maintenance and upgrade headache thereafter. If we're implementing a hint alternative, we should look at stuff in this priority order: 1. Useful tuning of additional cost parameters by GUC (i.e. cursor_tuple_fraction) 2. Modifying cost parameters on database *objects* (i.e. "ndistinct=500") 3. Adding new parameters to modify on database objects (i.e. "distribution=normal(1.5,17)","new_rows=0.1") 4. Query hints (if all of the above fails to give fixes for some tested problem) > Where exactly are the problems with other systems noted? Most other > systems have this option so saying "They have problems" is a giant cop > out. I've put my list down: http://wiki.postgresql.org/wiki/OptimizerHintsDiscussion#Problems_with_existing_Hint_stystems -- -- Josh Berkus PostgreSQL Experts Inc. http://www.pgexperts.com -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
