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SortExec: use merge sort for long keys to reduce number of comparison #1096

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Merged
lihao712 merged 1 commit into from
Aug 5, 2025
Merged

SortExec: use merge sort for long keys to reduce number of comparison #1096

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18 changes: 14 additions & 4 deletions native-engine/datafusion-ext-plans/src/sort_exec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -628,16 +628,26 @@ impl ExternalSorter {
self.mem_total_size
.fetch_add(batch.get_batch_mem_size(), SeqCst);

// sort keys
// NOTE: we use stable merge sort for longer keys due to less comparison
let (keys, batch) = self.prune_sort_keys_from_batch.prune(batch)?;
let sorted_indices: Vec<u32> = (0..batch.num_rows() as u32)
.sorted_unstable_by_key(|&row_idx| unsafe {
let sorted_indices = if keys.size() / keys.num_rows() <= 8 {
(0..keys.num_rows() as u32).sorted_unstable_by_key(|&row_idx| unsafe {
// safety: bypass boundary and lifetime checking
std::mem::transmute::<_, &'static [u8]>(
keys.row_unchecked(row_idx as usize).as_ref(),
)
})
.take(self.limit)
.collect();
} else {
(0..keys.num_rows() as u32).sorted_by_key(|&row_idx| unsafe {
// safety: bypass boundary and lifetime checking
std::mem::transmute::<_, &'static [u8]>(
keys.row_unchecked(row_idx as usize).as_ref(),
)
})
}
.take(self.limit)
.collect::<Vec<_>>();

// build keys
let mut key_collector = InMemRowsKeyCollector::default();
Expand Down