Jefffrey commented on code in PR #19642:
URL: https://github.com/apache/datafusion/pull/19642#discussion_r2671099455
##########
datafusion/expr/src/udwf.rs:
##########
@@ -427,21 +440,130 @@ pub trait WindowUDFImpl: Debug + DynEq + DynHash + Send
+ Sync {
None
}
- /// If not causal, returns the effect this function will have on the window
+ /// Returns the effect this function has on limit pushdowns. See
[`LimitEffect`]
+ /// for more details.
+ ///
+ /// Defaults to [`LimitEffect::Unknown`].
fn limit_effect(&self, _args: &[Arc<dyn PhysicalExpr>]) -> LimitEffect {
LimitEffect::Unknown
}
}
-/// the effect this function will have on the limit pushdown
+/// The effect this function will have on limit pushdowns through a window
bound.
Review Comment:
I'm still not clear on what the future plan for this API is; are we planning
to remove or modify it to be more general? If so are there concrete plans for
this?
I could make the docstring a bit more general for example and move a lot of
it to the `LimitPushPastWindows` optimizer rule, but I still feel the enum
itself is very specific to the rule:
https://github.com/apache/datafusion/blob/102caeb2261c5ae006c201546cf74769d80ceff8/datafusion/expr/src/udwf.rs#L436-L446
- The variants already describe themselves in terms of the effects they have
on the limit
So making it more general when the code itself is already quite specific
seems wrong 🤔
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