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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2021/01/26 23:44:23 UTC
[GitHub] [spark] c21 opened a new pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
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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[GitHub] [spark] c21 commented on pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
c21 commented on pull request #31353:
URL: https://github.com/apache/spark/pull/31353#issuecomment-768887641
cc @maropu, thanks.
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[GitHub] [spark] maropu commented on a change in pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
maropu commented on a change in pull request #31353:
URL: https://github.com/apache/spark/pull/31353#discussion_r566069710
##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/ObjectAggregationIterator.scala
##########
@@ -158,7 +158,7 @@ class ObjectAggregationIterator(
processRow(buffer, newInput)
// The hash map gets too large, makes a sorted spill and clear the map.
- if (hashMap.size >= fallbackCountThreshold) {
+ if (hashMap.size >= fallbackCountThreshold && inputRows.hasNext) {
Review comment:
Ah, ok. I've checked the code and the fix looks reasonable.
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[GitHub] [spark] cloud-fan closed pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
cloud-fan closed pull request #31353:
URL: https://github.com/apache/spark/pull/31353
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[GitHub] [spark] c21 commented on pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
c21 commented on pull request #31353:
URL: https://github.com/apache/spark/pull/31353#issuecomment-767903889
cc @cloud-fan could you help take a look? Thanks.
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[GitHub] [spark] c21 commented on pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
c21 commented on pull request #31353:
URL: https://github.com/apache/spark/pull/31353#issuecomment-769258569
Thank you @maropu and @cloud-fan for review!
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[GitHub] [spark] c21 commented on pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
c21 commented on pull request #31353:
URL: https://github.com/apache/spark/pull/31353#issuecomment-769258360
> btw, '0' above is just a typo?
@maropu - It was meant to be a link, I was typing `[0]` to give a reference link. Sorry for confusion.
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[GitHub] [spark] maropu commented on pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
maropu commented on pull request #31353:
URL: https://github.com/apache/spark/pull/31353#issuecomment-769032012
> ...based on number of keys seen so far 0.
btw, '`0`' above is just a typo?
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[GitHub] [spark] cloud-fan commented on pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on pull request #31353:
URL: https://github.com/apache/spark/pull/31353#issuecomment-769157058
thanks, merging to master!
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[GitHub] [spark] AmplabJenkins commented on pull request #31353: [SPARK-34253][SQL] Object hash aggregate should not fallback if no more input rows
Posted by GitBox <gi...@apache.org>.
AmplabJenkins commented on pull request #31353:
URL: https://github.com/apache/spark/pull/31353#issuecomment-767925915
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