marshauf opened a new pull request, #6713:
URL: https://github.com/apache/arrow-datafusion/pull/6713
# Which issue does this PR close?
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Closes #6518.
# Rationale for this change
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This change provides an example on how to replace a ScalarUDF node with a
user defined extension node. The node calls an async function on execution.
# What changes are included in this PR?
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It only adds another example which can be run with `cargo run --example
async_udf`.
# Are these changes tested?
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I ran `cargo run --example async_udf` which ran the example to completion
without an error. Example has no external dependencies towards its environment.
# Are there any user-facing changes?
No user facing changes.
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# TODO
At the moment the optimizer rule replaces the complete Projection. I would
like to just replace the Expr::ScalarUDF with a Expr::ScalarSubquery or
something similar which allows me to host the user defined extension node.
An example implementation is `rewrite_expr`, but Expr::ScalarSubquery
doesn't support LogicalPlan::Extension as a subquery. A function returns an
error at
https://github.com/apache/arrow-datafusion/blob/main/datafusion/optimizer/src/scalar_subquery_to_join.rs#L219-L219
because
https://github.com/apache/arrow-datafusion/blob/main/datafusion/expr/src/logical_plan/plan.rs#L411-L411
returns None for LogicalPlan::Extension.
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