tustvold commented on code in PR #4301:
URL: https://github.com/apache/arrow-datafusion/pull/4301#discussion_r1028358218
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datafusion/core/src/physical_plan/sorts/sort_preserving_merge.rs:
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@@ -570,45 +606,57 @@ impl SortPreservingMergeStream {
let _timer = elapsed_compute.timer();
loop {
- match self.heap.pop() {
- Some(Reverse(mut cursor)) => {
- let stream_idx = cursor.stream_idx();
- let batch_idx = self.batches[stream_idx].len() - 1;
- let row_idx = cursor.advance();
-
- let mut cursor_finished = false;
- // insert the cursor back to heap if the record batch is
not exhausted
- if !cursor.is_finished() {
- self.heap.push(Reverse(cursor));
- } else {
- cursor_finished = true;
- self.cursor_finished[stream_idx] = true;
+ // Adjust the loser tree if necessary
+ if !self.loser_tree_adjusted {
+ let mut winner = self.loser_tree[0];
Review Comment:
It might be easier to follow if this was moved into a method called
`replace_loser_tree_winner`, perhaps with a link to this GIF -
https://en.wikipedia.org/wiki/K-way_merge_algorithm#/media/File:Loser_tree_replacement_selection.gif
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