Andrew Lamb created ARROW-11689:
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Summary: [Rust][DataFusion] Reduce copies in DataFusion
LogicalPlan and Expr creation
Key: ARROW-11689
URL: https://issues.apache.org/jira/browse/ARROW-11689
Project: Apache Arrow
Issue Type: New Feature
Reporter: Andrew Lamb
The theme of this overall epic to make the plan and expression rewriting phases
of DataFusion more efficient by avoiding copies by leveraging the Rust type
system
Benefits:
* More standard / idomatic Rust usage
* faster / more efficient (I don't have numbers to back this up)
Downsides:
* These will be backwards incompatible changes
h1. Background
Many things in DataFusion look like
Input --tranformation-->output
And the input is not used again. In rust, you can model this by giving
ownership to the transformation
At a high level the idea is to avoid so much cloning in DataFustion
The basic principle is if the function needs to `clone` one of its arguments,
the caller should be given the choice of when to do that. Often, the caller can
give up ownership without issue
I envision at least the following the following items:
1. Optimizer passes that take `&LogicalPlan` and produce a new `LogicalPlan`
even though most callsites do not need the original
2. Expr builder calls that take `&expr` and return a new `Expr`
3. An expression rewriter (TODO) while running down optimizer passes
I think this style takes advantage of Rust's ownership model and will let us
avoid a lot o copying and allocations and avoid the need for something like
slab allocators
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