While all the talk of a hinting system over in hackers and perform is good, and I have a few queries that could live with a simple hint system pop up now and again, I keep thinking that a query planner that learns from its mistakes over time is far more desirable. Is it reasonable or possible for the system to have a way to look at query plans it's run and look for obvious mistakes its made, like being off by a factor of 10 or more in estimations, and slowly learn to apply its own hints? Seems to me that would be far more useful than my having to babysit the queries that are running slow and come up with hints to have the database do what I want. I already log slow queries and review them once a week by running them with explain analyze and adjust what little I can, like stats targets and such. It seems to me the first logical step would be having the ability to flip a switch and when the postmaster hits a slow query, it saves both the query that ran long, as well as the output of explain or explain analyze or some bastardized version missing some of the inner timing info. Even just saving the parts of the plan where the planner thought it would get 1 row and got instead 350,000 and was using a nested loop to join would be VERY useful. I could see something like that eventually evolving into a self tuning system. Well, I'm busy learning to be an Oracle DBA right now, so I can't do it. But it would be a very cool project for the next college student who shows up looking for one.
