Thanks all of you for your feedback. On Fri, May 29, 2020 at 9:04 AM Tom Lane <t...@sss.pgh.pa.us> wrote:
> Tomas Vondra <tomas.von...@2ndquadrant.com> writes: > > On Wed, May 27, 2020 at 09:58:04PM +0800, Andy Fan wrote: > >> so we need to optimize the cost model for such case, the method is the > >> patch I mentioned above. > > > Making the planner more robust w.r.t. to estimation errors is nice, but > > I wouldn't go as far saying we should optimize for such cases. > > Yeah, it's a serious mistake to try to "optimize" for cases where we have > no data or wrong data. By definition, we don't know what we're doing, > so who's to say whether we've made it better or worse? Actually I think it is a more robust way.. the patch can't fix think all the impact of bad statistics(That is impossible I think), but it will make some simple things better and make others no worse. By definition I think I know what we are doing here, like what I replied to Tomas above. But it is possible my think is wrong. > The other serious error we could be making here is to change things on > the basis of just a few examples. You really need a pretty wide range > of test cases to be sure that you're not making things worse, any time > you're twiddling basic parameters like these. > > I will try more thing with this direction, thanks for suggestion. -- Best Regards Andy Fan
