> I actually think the way to attack this issue is to discuss the kinds of errors the planner makes, and what tweaks we could do to correct them. > Here's the ones I'm aware of: > > -- Incorrect selectivity of WHERE clause > -- Incorrect selectivity of JOIN > -- Wrong estimate of rows returned from SRF > -- Incorrect cost estimate for index use > > Can you think of any others? I think your points are too generic, there is no way to get them all 100% correct from statistical data even with data hints (and it is usually not at all necessary for good enough plans). I think we need to more precisely define the problems of our system with point in time statistics -- no reaction to degree of other concurrent activity -- no way to react to abnormal skew that only persists for a very short duration -- too late reaction to changing distribution (e.g. current date column when a new year starts) and the variant: too late adaption when a table is beeing filled -- missing cost/selectivity estimates for several parts of the system Andreas
