[GitHub] [arrow] alamb commented on a change in pull request #8503: ARROW-10366: [Rust] [DataFusion] Remove collect from within threads on merge

[GitBox <gi...@apache.org>]

alamb commented on a change in pull request #8503:
URL: https://github.com/apache/arrow/pull/8503#discussion_r510061337



##########
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:
       I wonder if picking a fixed channel size might be a good idea. Specifically, given there is s one  That way the producers can't get too far ahead. I think a small fixed number (`number_of_cores`? 10?) might be reasonable to begin with
   
   Given that the actual work of `MergeStream` is pretty light (simply passing the record batches on) this may not be a problem in practice, but it probably depends on what order the tasks are run.




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