jorgecarleitao commented on a change in pull request #8503:
URL: https://github.com/apache/arrow/pull/8503#discussion_r510134213
##########
File path: rust/datafusion/src/physical_plan/merge.rs
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@@ -103,37 +105,56 @@ impl ExecutionPlan for MergeExec {
self.input.execute(0).await
}
_ => {
- let tasks = (0..input_partitions).map(|part_i| {
+ let (sender, receiver) =
mpsc::unbounded::<ArrowResult<RecordBatch>>();
Review comment:
Good point.
I actually started with a `bounded(1)`, but this (and other values) won't
work because we need to `join_all` threads. because there is no consumer to
retrieve the items from the `receiver`, we are locked as the threads cannot be
joined, and we wait indefinitely for the `join_all`.
An alternative is to not `join_all`, but then we risk losing results if the
main thread finishes first.
I.e. if we bound the channel, we cannot `join_all` and thus we may lose
threads. If we join all, the channel needs to be unbounded so that we can build
the stream.
IMO neither is good, as in both cases we are essentially waiting for all
threads to finish before returning the stream, which I understand is not what
we want.
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