cloud-fan opened a new pull request #32594:
URL: https://github.com/apache/spark/pull/32594
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### What changes were proposed in this pull request?
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This PR improves the interaction between partition coalescing and skew
handling by moving the skew join rule ahead of the partition coalescing rule
and making corresponding changes to the two rules:
1. Simplify `OptimizeSkewedJoin` as it doesn't need to handle
`CustomShuffleReaderExec` anymore.
2. Update `CoalesceShufflePartitions` to support coalescing non-skewed
partitions.
### Why are the changes needed?
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It's a bit hard to reason about skew join if partitions have been coalesced.
A skewed partition needs to be much larger than other partitions and we need to
look at the raw sizes before coalescing.
It also makes `OptimizeSkewedJoin` more robust, as we don't need to worry
about a skewed partition being coalesced with a small partition and breaks skew
join handling.
It also helps with https://github.com/apache/spark/pull/31653 , which needs
to move `OptimizeSkewedJoin` to an earlier phase and run before
`CoalesceShufflePartitions`.
### Does this PR introduce _any_ user-facing change?
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No
### How was this patch tested?
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new UT and existing tests
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