On Wed, Jan 2, 2019 at 6:19 PM Tomas Vondra <tomas.von...@2ndquadrant.com> wrote:
> After looking at the "FETCH FIRST ... PERCENT" patch, I wonder if this > patch should tweak estimates in some way. Currently, the cardinality > estimate is the same as for plain LIMIT, using the requested number of > rows. But let's say there are very few large groups - that will > naturally increase the number of rows produced. > > As an example, let's say the subplan produces 1M rows, and there are > 1000 groups (when split according to the ORDER BY clause). > can we use ORDER BY column raw statistic in limit node reliably? because it seems to me it can be affected by other operation in a subplan like filter condition regards Surafel
