neilconway commented on code in PR #20672:
URL: https://github.com/apache/datafusion/pull/20672#discussion_r2884372912
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datafusion/physical-plan/src/spill/spill_pool.rs:
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@@ -1343,6 +1368,88 @@ mod tests {
Ok(())
}
+ /// Regression test for data loss when multiple writer clones are used.
+ ///
+ /// `SpillPoolWriter` is `Clone`, and in non-preserve-order repartitioning
+ /// mode all input partition tasks share clones of the same writer. Before
+ /// the fix, `Drop` unconditionally set `writer_dropped = true` even when
+ /// other clones were still alive. This caused the `SpillPoolReader` to
+ /// return EOF prematurely, silently losing every batch written by the
+ /// remaining writers.
Review Comment:
[ Nit, optional ] I personally try to avoid comments that are very specific
to the previous (buggy) implementation, because that implementation won't exist
for future readers, and the current / future state of the code might drift
without the comments being updated. So I'd personally remove references to "the
bug" or the exact previous behavior, and talk more about what a correct
implementation ought to do and the properties of a correct implementation that
we're checking for.
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