On Mon, 4 Mar 2024 at 19:20, Andrei Lepikhov <a.lepik...@postgrespro.ru> wrote: > Could we use the trick with the get_actual_variable_range() to find some > reason and extrapolate histogram data out of the boundaries when an > index shows us that we have min/max outside known statistics? > Because it would be used for the values out of the histogram, it should > only add an overhead with a reason.
I think, in theory, it would be possible to add a function similar to get_actual_variable_range() for equality clauses, but I'd be worried about the overheads of doing so. I imagine it would be much more common to find an equality condition with a value that does not fit in any histogram/MCV bucket. get_actual_variable_range() can be quite costly when there are a large number of tuples ready to be vacuumed, and having an equivalent function for equality conditions could appear to make the planner "randomly" slow without much of an explanation as to why. I think we still do get some complaints about get_actual_variable_range() despite it now using SnapshotNonVacuumable. It used to be much worse with the snapshot type it used previous to what it uses today. IIRC it took a few iterations to get the performance of the function to a level that seems "mostly acceptable". David
