2010YOUY01 commented on code in PR #15700:
URL: https://github.com/apache/datafusion/pull/15700#discussion_r2191376010
##########
datafusion/physical-plan/src/aggregates/row_hash.rs:
##########
@@ -1067,14 +1074,13 @@ impl GroupedHashAggregateStream {
sort_batch(&batch, &expr, None)
})),
)));
- for spill in self.spill_state.spills.drain(..) {
- let stream =
self.spill_state.spill_manager.read_spill_as_stream(spill)?;
- streams.push(stream);
- }
+
self.spill_state.is_stream_merging = true;
self.input = StreamingMergeBuilder::new()
.with_streams(streams)
.with_schema(schema)
+ .with_spill_manager(self.spill_state.spill_manager.clone())
+ .with_sorted_spill_files(std::mem::take(&mut
self.spill_state.spills))
Review Comment:
I suggest to spill all in-memory batches (in `streams`) to disk, before this
final merging step. Also, let the multi pass merge operator also only handle
spill files, and don't have to handle in-mem batches and spills at the same
time.
This is just a simplification for now, we can do a optimization to avoid
this re-spill step in the future.
The issue is, without special handling, it's possible that in-mem batches
will take most of the available memory budget, and leave only a very small
memory part for multi-pass spilling to continue. This can cause slow downs or
even prevent some cases to finish.
We're already doing this in sort executor, see:
https://github.com/apache/datafusion/blob/14487ddc275fc1f148f339293664fe7f83d91d09/datafusion/physical-plan/src/sorts/sort.rs#L336-L341
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