On Thu, May 5, 2022 at 7:03 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > I wrote: > > I instrumented the code in setrefs.c, and found that during the > > core regression tests this patch estimates correctly in 2103 > > places while guessing wrongly in 54, so that seems like a pretty > > good step forward. > > On second thought, that's not a terribly helpful summary. Breaking > things down to the next level, there were > > 1088 places where we correctly guessed a subquery isn't trivial > (so no change from current behavior, which is correct) > > 1015 places where we correctly guessed a subquery is trivial > (hence, improving the cost estimate from before) > > 40 places where we incorrectly guessed a subquery isn't trivial > (so no change from current behavior, although that's wrong) > > 14 places where we incorrectly guessed a subquery is trivial > (hence, incorrectly charging zero for the SubqueryScan) > > 1015 improvements to 14 disimprovements isn't a bad score. I'm > a bit surprised there are that many removable SubqueryScans TBH; > maybe that's an artifact of all the "SELECT *" queries. >
The patch looks sane to me. 1015 vs 14 is a good win. Thanks Richard
