On 26 March 2018 at 14:08, Tomas Vondra <tomas.von...@2ndquadrant.com> wrote: > On 03/26/2018 12:31 PM, Dean Rasheed wrote: >> A wider concern I have is that I think this function is trying to be >> too clever by only resetting selected stats. IMO it should just reset >> all stats unconditionally when the column type changes, which would >> be consistent with what we do for regular stats. >> > The argument a year ago was that it's more plausible that the semantics > remains the same. I think the question is how the type change affects > precision - had the type change in the opposite direction (int to real) > there would be no problem, because both ndistinct and dependencies would > produce the same statistics. > > In my experience people are far more likely to change data types in a > way that preserves precision, so I think the current behavior is OK.
Hmm, I don't really buy that argument. Altering a column's type allows the data in it to be rewritten in arbitrary ways, and I don't think we should presume that the statistics will still be valid just because the user *probably* won't do something that changes the data much. Regards, Dean
