allisonwang-db opened a new pull request #29031:
URL: https://github.com/apache/spark/pull/29031
### What changes were proposed in this pull request?
This PR added a physical rule to remove redundant project nodes. A
`ProjectExec` is redundant when
1. It has the same output attributes and order as its child's output when
ordering of these attributes is required.
2. It has the same output attributes as its child's output when attribute
output ordering is not required.
For example:
After Filter:
```
== Physical Plan ==
*(1) Project [a#14L, b#15L, c#16, key#17]
+- *(1) Filter (isnotnull(a#14L) AND (a#14L > 5))
+- *(1) ColumnarToRow
+- FileScan parquet [a#14L,b#15L,c#16,key#17]
```
The `Project a#14L, b#15L, c#16, key#17` is redundant because its output is
exactly the same as filter's output.
Before Aggregate:
```
== Physical Plan ==
*(2) HashAggregate(keys=[key#17], functions=[sum(a#14L), last(b#15L,
false)], output=[sum_a#39L, key#17, last_b#41L])
+- Exchange hashpartitioning(key#17, 5), true, [id=#77]
+- *(1) HashAggregate(keys=[key#17], functions=[partial_sum(a#14L),
partial_last(b#15L, false)], output=[key#17, sum#49L, last#50L, valueSet#51])
+- *(1) Project [key#17, a#14L, b#15L]
+- *(1) Filter (isnotnull(a#14L) AND (a#14L > 100))
+- *(1) ColumnarToRow
+- FileScan parquet [a#14L,b#15L,key#17]
```
The `Project key#17, a#14L, b#15L` is redundant because hash aggregate
doesn't require child plan's output to be in a specific order.
### Why are the changes needed?
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1. If you propose a new API, clarify the use case for a new API.
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It removes unnecessary query nodes and makes query plan cleaner.
### Does this PR introduce _any_ user-facing change?
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the documentation fix.
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behavior difference if possible.
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No
### How was this patch tested?
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Unit tests
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