On Wed, Apr 03, 2019 at 03:08:05PM -0400, Tom Lane wrote:
Tomas Vondra <tomas.von...@2ndquadrant.com> writes:
I've tried to fix the merge conflict (essentially by moving some of the
code to adjust_limit_rows_costs(), but I'm wondering if the code added to
create_limit_path is actually correct
...
Firstly, this seriously needs some comment explaining why we do this.
I've not looked at this patch, but TBH I wonder why it is touching
planner rowcount estimation at all. I find it doubtful either that
a correction for WITH TIES would be significant in most use-cases,
or that we could estimate it accurately if it was significant.
It certainly doesn't seem like something that needs to be messed
with in v1 of the feature.
FWIW it was me who suggested to tweak the cardinality estimation this way,
but if we want to leave it out from v1, I'm OK with that.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
