MassivePizza commented on code in PR #10364:
URL: https://github.com/apache/arrow-rs/pull/10364#discussion_r3615872563
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parquet/src/arrow/arrow_writer/mod.rs:
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@@ -1834,14 +1834,15 @@ fn get_interval_ym_array_slice(
array: &arrow_array::IntervalYearMonthArray,
indices: impl ExactSizeIterator<Item = usize>,
) -> Vec<FixedLenByteArray> {
- let mut values = Vec::with_capacity(indices.len());
+ const VALUE_SIZE: usize = 12;
+ let mut arena = Vec::with_capacity(indices.len() * VALUE_SIZE);
for i in indices {
- let mut value = array.value(i).to_le_bytes().to_vec();
- let mut suffix = vec![0; 8];
- value.append(&mut suffix);
- values.push(FixedLenByteArray::from(ByteArray::from(value)))
+ let mut out = [0; 12];
+ let value = array.value(i);
+ out[0..4].copy_from_slice(&value.to_le_bytes());
+ arena.extend_from_slice(&out);
Review Comment:
Looked at the codegen, and it avoided some XORs. The real benefit came from
rewriting it to use `chunks_exact_mut` (see
https://github.com/apache/arrow-rs/pull/10364/changes/baa13dd29c458595eb6913fc2a24885309cbf6c1).
And I preferred the per-value XOR above a zeroed alloc, since the chunk is
being filled linearly anyway.
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