Rich-T-kid commented on code in PR #27025:
URL: https://github.com/apache/datafusion/pull/27025#discussion_r4455721999
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datafusion/common/src/hash_utils.rs:
##########
@@ -158,8 +181,14 @@ where
let mut buffer = cell.try_borrow_mut()
.map_err(|_| _internal_datafusion_err!("with_hashes cannot be
called reentrantly on the same thread"))?;
- // Ensure buffer has sufficient length, clearing old values
- buffer.clear();
+ // A dictionary with non-null keys and values overwrites every output
+ // slot, so retain the initialized storage instead of zeroing it first.
Review Comment:
Fixed in 0a7c4da0c. The reuse gate now uses the cheap conservative
Dictionary plus !is_nullable() check, avoiding the extra dictionary downcast
and duplicate null-count pair.
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datafusion/common/src/hash_utils.rs:
##########
@@ -2284,6 +2368,78 @@ mod tests {
assert_eq!(result, expected_hashes);
}
+ #[test]
+ #[cfg(not(feature = "force_hash_collisions"))]
Review Comment:
Addressed in 0a7c4da0c with a brief comment: PrimitiveArray::values()
already accounts for slices, and every dictionary key width uses the same
generic as_usize lookup, so neither changes the fast-path invariant.
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