On Fri, 22 Mar 2019 at 11:39, Tom Lane <t...@sss.pgh.pa.us> wrote: > Simon Riggs <si...@2ndquadrant.com> writes: > > I agree that the issue of mixing sorts at various points will make > nonsense > > of the startup cost/total cost results. > > Right. > > > I don't see LIMIT costing being broken as a reason to restrict this > > optimization. I would ask that we allow improvements to the important use > > case of ORDER BY/LIMIT, then spend time on making LIMIT work correctly. > > There's not time to reinvent LIMIT costing for v12. I'd be happy to > see some work done on that in the future, and when it does get done, > I'd be happy to see Append planning extended to allow this case. > I just don't think it's wise to ship one without the other. >
I was hoping to motivate you to look at this personally, and soon. LIMIT is so broken that any improvements count as bug fixes in my book. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
