On Sun, Apr 3, 2016 at 7:18 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Alex Shulgin <alex.shul...@gmail.com> writes: > > On Sun, Apr 3, 2016 at 3:43 AM, Alex Shulgin <alex.shul...@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? >
Well, what implies that the last value is somehow special? I would think we should just do with it whatever we do with the rest of the candidate MCVs. For "the only value" case: we cannot build a histogram out of a single value, so omitting it from MCVs is not a good strategy, ISTM. >From my point of view that amounts to "include always". What problems do you see with this approach exactly? -- Alex
