tustvold commented on PR #4767:
URL:
https://github.com/apache/arrow-datafusion/pull/4767#issuecomment-1367945554
> One thing I wonder about is what happens if the same rule is run multiple
times?
This will be fine, there is a potential collision if the same rule appears
multiple times in the same list of optimizers, i.e. something like
```
let rules: Vec<Arc<dyn OptimizerRule + Sync + Send>> = vec![
Arc::new(DecorrelateWhereIn::new()),
Arc::new(ScalarSubqueryToJoin::new()),
Arc::new(ScalarSubqueryToJoin::new()),
...
];
```
However, this doesn't occur in practice and could easily be worked around by
using
```
let subquery = Arc::new(ScalarSubqueryToJoin::new());
let rules: Vec<Arc<dyn OptimizerRule + Sync + Send>> = vec![
Arc::new(DecorrelateWhereIn::new()),
subquery.clone(),
subquery,
...
];
```
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