On Fri, May 1, 2015 at 3:30 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Assuming that that sketch is accurate, it would take more code to provide > a new user-visible knob to enable/disable the behavior than it would to > implement the optimization, which makes me pretty much -1 on providing > such a knob. We should either do it or not. If we do, people who want > optimization fences should use the traditional "OFFSET 0" hack. > > (A possible compromise position would be to offer a new GUC to > enable/disable the optimization globally; that would add only a reasonably > small amount of control code, and people who were afraid of the change > breaking their apps would probably want a global disable anyway.)
+1 to both. The default should be to allow the user to choose between CTE and inline subqueries for style reasons alone - as much as possible since you cannot have a correlated CTE nor a recursive subquery. Trust in the planner, the planner is good. If it isn't then requiring OFFSET 0 as the only means to create an optimization fence seems reasonable. I like the GUC as an cheap means to keep the status-quo for those who desire it. While the idea of overriding the status-quo on a per-query basis has some appeal the apparent cost-benefit ratio doesn't seem convincing. David J.
