UBarney commented on code in PR #19411:
URL: https://github.com/apache/datafusion/pull/19411#discussion_r2672453954
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datafusion/physical-plan/src/joins/hash_join/exec.rs:
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@@ -168,6 +249,34 @@ impl JoinLeftData {
/// `<col1> != <col2>`) are known as "filter expressions" and are evaluated
/// after the equijoin predicates.
///
+/// # ArrayMap Optimization
+///
+/// For joins with a single integer-based join key, `HashJoinExec` may use an
[`ArrayMap`]
+/// (also known as a "perfect hash join") instead of a general-purpose hash
map.
+/// This optimization is used when:
+/// 1. There is exactly one join key.
+/// 2. The join key can be any integer type convertible to u64 (excluding i128
and u128).
Review Comment:
I've applied the suggested change
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