kazuyukitanimura commented on code in PR #8004:
URL: https://github.com/apache/arrow-datafusion/pull/8004#discussion_r1378633704
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datafusion/physical-plan/src/aggregates/row_hash.rs:
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@@ -673,7 +673,16 @@ impl GroupedHashAggregateStream {
let spillfile =
self.runtime.disk_manager.create_tmp_file("HashAggSpill")?;
let mut writer = IPCWriter::new(spillfile.path(), &emit.schema())?;
// TODO: slice large `sorted` and write to multiple files in parallel
- writer.write(&sorted)?;
+ let mut offset = 0;
+ let total_rows = sorted.num_rows();
+
+ while offset < total_rows {
+ let length = std::cmp::min(total_rows - offset, self.batch_size);
+ let batch = sorted.slice(offset, length);
+ offset += batch.num_rows();
+ writer.write(&batch)?;
+ }
+
Review Comment:
Got it.
Would you mind explaining how reading smaller files reduces memory usage? I
thought we are streaming when reading back for merging. Also, when merge-sort
is going on, we need to open all files anyway? Just making sure the original
issue statement in #8003
Additionally, I think we have to create a new writer otherwise, we keep
appending to the same temp file? So we end up having the same file size?
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