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From Jacques Nadeau <jacq...@apache.org>
Subject Re: ProjectMergeRule
Date Tue, 21 Jul 2015 19:17:29 GMT
After much discussion last year, I'm entirely in support of Julian's
abstract goals.  However, I'm concerned about the real world impact.

On Tue, Jul 21, 2015 at 12:09 PM, Julian Hyde <jhyde@apache.org> wrote:

> 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
> <sitnikov.vladimir@gmail.com> 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
>

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