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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Beginne damit, die bestehende Diskussion zum Optimizer und das in issue #440 referenzierte experimentelle egg-basierte Optimizer-Framework zu lesen. Vergleiche, wie Traversierung, Pattern Matching und Rewriting behandelt werden, und kläre anschließend mit den Maintainer:innen das gewünschte Framework und den Umfang; dieses Issue definiert kein konkretes Abschlusskriterium.

Vom Indexierungsmodell aus dem Issue-Text verfasst.