> By the way, wouldn't it be possible if the planner learned from a query > execution, so it would know if a choice for a specific plan or estimate > was actually correct or not for future reference? Or is that in the line > of DB2's complexity and a very hard problem and/or would it add too much > overhead? Just thinking out-loud here... Wow, a learning cost based planner sounds a-lot like problem for control & dynamical systems theory. As I understand it, much of the advice given for setting PostgreSQL's tune-able parameters are from "RULES-OF-THUMB." I am sure that effect on server performance from all of the parameters could be modeled and an adaptive feed-back controller could be designed to tuned these parameters as demand on the server changes. Al-thought, I suppose that a controller like this would have limited success since some of the most affective parameters are non-run-time tune-able. In regards to query planning, I wonder if there is way to model a controller that could adjust/alter query plans based on a comparison of expected and actual query execution times. Regards, Richard Broersma Jr.
