DataFusion Optimizer framework discussion

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Current DataFusion's optimizer rules are complex and not easy to implement. I think one of the reason is each optimization rule has to deal with the plan tree traversing, pattern matching and rewriting. It is more a visitor model (like the old Presto optimizer rules).
And if we add new logical plan nodes, especially non-leaf plan nodes, it is very possible that all the rules need to be modified to add the related visit logic.

An alternative approach is we can have the Optimizer itself drive the plan tree traversing and apply the rules down/up the tree, it will make the rule logic much clear and can focus on pattern matching and rewriting.

I see there is a new experimental optimizer framework which leverages the egg lib.
https://github.com/apache/arrow-datafusion/issues/440
I'm not familiar with egg and not sure how mature the egg lib is.

Please share your thoughts.

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Inizia leggendo la discussione esistente sull’optimizer e il framework sperimentale di ottimizzazione basato su egg a cui si fa riferimento in issue #440. Confronta il modo in cui vengono gestiti il traversal, il pattern matching e il rewriting, quindi chiarisci con i maintainer il framework e l’ambito desiderati; questa issue non definisce un criterio concreto di completamento.

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