yjshen commented on code in PR #7180:
URL: https://github.com/apache/arrow-datafusion/pull/7180#discussion_r1286412463
##########
datafusion/core/src/physical_plan/sorts/sort.rs:
##########
@@ -253,11 +256,19 @@ impl ExternalSorter {
/// Appends an unsorted [`RecordBatch`] to `in_mem_batches`
///
/// Updates memory usage metrics, and possibly triggers spilling to disk
- async fn insert_batch(&mut self, input: RecordBatch) -> Result<()> {
+ async fn insert_batch(&mut self, mut input: RecordBatch) -> Result<()> {
if input.num_rows() == 0 {
return Ok(());
}
+ let mut batch_sorted = false;
+ if self.fetch.map_or(false, |f| f < input.num_rows()) {
Review Comment:
I'm thinking can we make the heuristic `f < input.num_rows() / 10` or
something magic numbers to only do eager sort for small `K's?
##########
datafusion/core/src/physical_plan/sorts/sort.rs:
##########
@@ -639,15 +614,47 @@ fn write_sorted(
Ok(())
}
-fn read_spill(sender: Sender<Result<RecordBatch>>, path: &Path) -> Result<()> {
+/// Stream batches from spill files.
+///
+/// Each spill file has one or more batches. Intra-batch order is guaranteed
(each one is sorted),
+/// but the inter-batch ordering is not guaranteed, hence why we need to
convert each batch from the
+/// spill to a separate input stream for the merge-sort procedure.
Review Comment:
Will this produce unnecessary comparison when the inter-batch ordering is
guaranteed for the normal case without `K`?
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