Rich-T-kid commented on code in PR #27025:
URL: https://github.com/apache/datafusion/pull/27025#discussion_r4456072306
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datafusion/common/src/hash_utils.rs:
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@@ -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
Review Comment:
Direct A/B: restoring `buffer.clear()` was 1.04x slower for multiple
dictionaries (10.4 vs. 10.0 µs) and 1.16x slower for a single dictionary (3.2
vs. 2.8 µs). I think that win is worth keeping now that the overwrite invariant
is covered by the debug checks. Kept the skip in `90f551c9c`.
[Run](https://github.com/apache/datafusion/pull/27025#issuecomment-6606411962).
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