Re: More stable query plans via more predictable column statistics

Alex Shulgin <alex.shulgin@gmail.com> writes:
> On Sun, Apr 3, 2016 at 3:43 AM, Alex Shulgin <alex.shulgin@gmail.com> wrote:
>> I'm not sure yet about the 1% rule for the last value, but would also love
>> to see if we can avoid the arbitrary limit here.  What happens with a last
>> value which is less than 1% popular in the current code anyway?

> Now that I think about it, I don't really believe this arbitrary heuristic
> is any good either, sorry.

Yeah, it was just a placeholder to produce a working patch.

Maybe we could base this cutoff on the stats target for the column?
That is, "1%" would be the right number if stats target is 100,
otherwise scale appropriately.

> What was your motivation to introduce some limit at the bottom anyway?

Well, we have to do *something* with the last (possibly only) value.
Neither "include always" nor "omit always" seem sane to me.  What other
decision rule do you want there?
        regards, tom lane