Kontinuation commented on code in PR #1511:
URL: https://github.com/apache/datafusion-comet/pull/1511#discussion_r2017870588
##########
native/core/src/execution/shuffle/shuffle_writer.rs:
##########
@@ -422,27 +432,29 @@ impl ShuffleRepartitioner {
.collect::<Result<Vec<_>>>()?;
// use identical seed as spark hash partition
- let hashes_buf = &mut self.hashes_buf[..arrays[0].len()];
+ let hashes_buf = &mut
scratch.hashes_buf[..arrays[0].len()];
hashes_buf.fill(42_u32);
// Hash arrays and compute buckets based on number of
partitions
- let partition_ids = &mut
self.partition_ids[..arrays[0].len()];
+ let partition_ids = &mut
scratch.partition_ids[..arrays[0].len()];
create_murmur3_hashes(&arrays, hashes_buf)?
.iter()
.enumerate()
.for_each(|(idx, hash)| {
- partition_ids[idx] = pmod(*hash,
*num_output_partitions) as u64
+ partition_ids[idx] = pmod(*hash,
*num_output_partitions) as u32;
});
// count each partition size
- let mut partition_counters = vec![0usize;
*num_output_partitions];
+ let partition_counters = &mut scratch.partition_starts;
+ partition_counters.resize(num_output_partitions + 1, 0);
+ partition_counters.fill(0);
partition_ids
.iter()
.for_each(|partition_id|
partition_counters[*partition_id as usize] += 1);
// accumulate partition counters into partition ends
// e.g. partition counter: [1, 3, 2, 1] => [1, 4, 6, 7]
Review Comment:
Yes, this is an inclusive prefix sum. If we use `scan` and also avoids
allocating a new vector we have to write the following code, which is not much
readable than the current approach.
```rust
partition_ends.iter_mut().scan(0, |accum, v| {
*accum += *v;
Some(*accum)
}).enumerate().for_each(|(i, sum)| {
partition_ends[i] = sum;
});
```
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