Tomas Vondra <tomas.vondra@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.
