gabotechs commented on code in PR #23184:
URL: https://github.com/apache/datafusion/pull/23184#discussion_r3492179416
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datafusion/physical-expr/src/partitioning.rs:
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@@ -596,17 +642,39 @@ pub enum Distribution {
/// Requires children to be distributed in such a way that the same
/// values of the keys end up in the same partition
HashPartitioned(Vec<Arc<dyn PhysicalExpr>>),
+ /// Requires rows with equal values for the given keys to be colocated in
+ /// the same partition, without requiring a specific partitioning
algorithm.
+ ///
+ /// Unlike [`Self::HashPartitioned`], this can be satisfied by non-hash
+ /// partitioning such as range partitioning. A partitioning on a subset of
+ /// these keys can also satisfy this requirement because rows equal on all
+ /// required keys are also equal on any subset.
+ ///
+ /// For multi-input operators, satisfaction alone is not enough: each input
+ /// may satisfy its own key requirement while using incompatible partition
+ /// boundaries. Use [`Partitioning::co_partitioned_with`] before pairing
+ /// partitions by index.
+ KeyPartitioned(Vec<Arc<dyn PhysicalExpr>>),
}
Review Comment:
For doing this incrementally, I imagine that if we keep both
`HashPartitioned` and `KeyPartitioned` alive while introducing the changes in
this PRs and the followings, you are going to be paying a high price in terms
of code for maintaining compatibility with both for something that is meant to
disappear right afterwards.
A cheaper option would be to rename `HashPartitioned` to `KeyPartitioned`
first, and then you would not need to pay the price of maintaining
compatibility with both.
I'd would not be surprised if you find out that renaming `HashPartitioned`
to `KeyPartitioned` is completely free without caveats.
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