alamb commented on code in PR #16322:
URL: https://github.com/apache/datafusion/pull/16322#discussion_r2135636293
##########
datafusion/physical-plan/src/sorts/merge.rs:
##########
@@ -216,36 +212,50 @@ impl<C: CursorValues> SortPreservingMergeStream<C> {
// Once all partitions have set their corresponding cursors for the
loser tree,
// we skip the following block. Until then, this function may be
called multiple
// times and can return Poll::Pending if any partition returns
Poll::Pending.
+
if self.loser_tree.is_empty() {
- while let Some(&partition_idx) =
self.uninitiated_partitions.front() {
+ // Manual indexing since we're iterating over the vector and
shrinking it in the loop
+ let mut idx = 0;
+ while idx < self.uninitiated_partitions.len() {
+ let partition_idx = self.uninitiated_partitions[idx];
match self.maybe_poll_stream(cx, partition_idx) {
Poll::Ready(Err(e)) => {
self.aborted = true;
return Poll::Ready(Some(Err(e)));
}
Poll::Pending => {
- // If a partition returns Poll::Pending, to avoid
continuously polling it
- // and potentially increasing upstream buffer sizes,
we move it to the
- // back of the polling queue.
- self.uninitiated_partitions.rotate_left(1);
-
- // This function could remain in a pending state, so
we manually wake it here.
- // However, this approach can be investigated further
to find a more natural way
- // to avoid disrupting the runtime scheduler.
- cx.waker().wake_by_ref();
- return Poll::Pending;
+ // The polled stream is pending which means we're
already set up to
+ // be woken when necessary
+ // Try the next stream
+ idx += 1;
}
_ => {
- // If the polling result is Poll::Ready(Some(batch))
or Poll::Ready(None),
- // we remove this partition from the queue so it is
not polled again.
- self.uninitiated_partitions.pop_front();
+ // The polled stream is ready
Review Comment:
thank you for these comments 👍
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