Yes, I do think these "little" relational expressions can have a very significant impact. They may block optimizations, they increase size of the search space (which makes the rule queue longer, and generates more GC pressure).
To be clear: it's perfectly fine if client programs (e.g the SqlToRelConverter) create these expressions. But the planner rules have to be ruthless in stripping them away. And the engine has to do a better job of ignoring them after they have been shown to be trivial. On Tue, Jul 21, 2015 at 11:55 AM, Vladimir Sitnikov <[email protected]> wrote: > I'm not sure if "field names for very top project" play any difference. > > As far as I understand, the intention was to keep execution plan readable. > > Julian, can you please highlight why are you thinking of merging > "project that merely renames"? > > Does it block another optimization? > Does it expand search space much? > Vladimir
