c21 opened a new pull request #31353:
URL: https://github.com/apache/spark/pull/31353
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### What changes were proposed in this pull request?
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Object hash aggregate will fallback to sort-based aggregation based on
number of keys seen so far [0]. The default config threshold is 128
(spark.sql.objectHashAggregate.sortBased.fallbackThreshold in [1]). There's an
edge case we can do better, where we do not fallback if there's no more input
rows. Suppose the task only has 128 group-by keys in hash ma, we don't need to
fallback in this case, and we can save the extra sort. This is an rare edge
case in production, but it can happen.
[0]:
https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/ObjectAggregationIterator.scala#L161
[1]:
https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala#L1615
### Why are the changes needed?
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To avoid unnecessary sort in query. Save resource.
### Does this PR introduce _any_ user-facing change?
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No.
### How was this patch tested?
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Add a unit test to verify task fallback or not is challenging. Given the
change is pretty minor, besides relying on existing test in
`ObjectHashAggregateSuite.scala`, I manually ran the followed query, and
verified in debug mode that the code path for fallback was not executed. And
verified the code path for fallback was executed without this change.
```
withSQLConf(
SQLConf.USE_OBJECT_HASH_AGG.key -> "true",
SQLConf.OBJECT_AGG_SORT_BASED_FALLBACK_THRESHOLD.key -> "1") {
Seq.fill(1)(Tuple1(Array.empty[Int]))
.toDF("c0")
.groupBy(lit(1))
.agg(typed_count($"c0"), max($"c0")).collect()
}
```
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