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[GitHub] [spark] tanelk opened a new pull request #31772: [SPARK-33851][SQL] Push partial aggregate bellow manually inserted repartition
tanelk opened a new pull request #31772:
URL: https://github.com/apache/spark/pull/31772
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### What changes were proposed in this pull request?
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Added physical optimization rule `PushDownAggregates`.
### Why are the changes needed?
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A common pattern I have encountered
```
dataset
.groupBy(col("a"), col("b")).count()
.groupBy(col("a")).agg(max("count"))
.explain();
```
Produces a plan:
```
*(3) HashAggregate(keys=[a#53], functions=[max(count#119L)])
+- Exchange hashpartitioning(a#53, 1), ENSURE_REQUIREMENTS, [id=#98]
+- *(2) HashAggregate(keys=[a#53], functions=[partial_max(count#119L)])
+- *(2) HashAggregate(keys=[a#53, b#52], functions=[count(1)])
+- Exchange hashpartitioning(a#53, b#52, 1), ENSURE_REQUIREMENTS, [id=#93]
+- *(1) HashAggregate(keys=[a#53, b#52], functions=[partial_count(1)])
+- FileScan parquet
```
In most cases the second exchange could be avoided if the first exchange partitioned only by column `a` - reducing the total amount of data exchanged. Spark can not do this optimization on its own, because `a` could have low cardinality (less than the number of executors) or high skew. But if the user knows, that this is not the case, they could manually repartition it:
```
dataset
.repartition(col("a"))
.groupBy(col("a"), col("b")).count()
.groupBy(col("a")).agg(max("count"))
.explain();
```
This produces this plan:
```
*(2) HashAggregate(keys=[a#53], functions=[max(count#119L)])
+- *(2) HashAggregate(keys=[a#53], functions=[partial_max(count#119L)])
+- *(2) HashAggregate(keys=[a#53, b#52], functions=[count(1)])
+- *(2) HashAggregate(keys=[a#53, b#52], functions=[partial_count(1)])
+- Exchange hashpartitioning(a#53, 1), REPARTITION, [id=#90]
+- FileScan parquet
```
We have avoided one exchange and this has had positive performance impact on my queries. But this could be improved further, if the first partial aggregate would be before the manually inserted repartition - reducing the exchanged data even more. The proposed rule would push that partial aggregate bellow the exchange.
### Does this PR introduce _any_ user-facing change?
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A configuration parameter to disable this optimization.
### How was this patch tested?
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[GitHub] [spark] AmplabJenkins commented on pull request #31772: [SPARK-33851][SQL] Push partial aggregate bellow manually inserted repartition
Posted by GitBox <gi...@apache.org>.
AmplabJenkins commented on pull request #31772:
URL: https://github.com/apache/spark/pull/31772#issuecomment-792362197
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[GitHub] [spark] SparkQA commented on pull request #31772: [SPARK-33851][SQL] Push partial aggregate bellow manually inserted repartition
Posted by GitBox <gi...@apache.org>.
SparkQA commented on pull request #31772:
URL: https://github.com/apache/spark/pull/31772#issuecomment-792359503
**[Test build #135845 has finished](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/135845/testReport)** for PR 31772 at commit [`1849fb8`](https://github.com/apache/spark/commit/1849fb812b4be3d2ae63bd649bde3ce220588858).
* This patch **fails Spark unit tests**.
* This patch merges cleanly.
* This patch adds no public classes.
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[GitHub] [spark] maropu commented on pull request #31772: [WIP][SPARK-33851][SQL] Push partial aggregate bellow manually inserted repartition
Posted by GitBox <gi...@apache.org>.
maropu commented on pull request #31772:
URL: https://github.com/apache/spark/pull/31772#issuecomment-792700370
Why this closed?
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[GitHub] [spark] tanelk closed pull request #31772: [WIP][SPARK-33851][SQL] Push partial aggregate bellow manually inserted repartition
Posted by GitBox <gi...@apache.org>.
tanelk closed pull request #31772:
URL: https://github.com/apache/spark/pull/31772
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[GitHub] [spark] SparkQA commented on pull request #31772: [SPARK-33851][SQL] Push partial aggregate bellow manually inserted repartition
Posted by GitBox <gi...@apache.org>.
SparkQA commented on pull request #31772:
URL: https://github.com/apache/spark/pull/31772#issuecomment-792344070
**[Test build #135845 has started](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/135845/testReport)** for PR 31772 at commit [`1849fb8`](https://github.com/apache/spark/commit/1849fb812b4be3d2ae63bd649bde3ce220588858).
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Posted by GitBox <gi...@apache.org>.
SparkQA removed a comment on pull request #31772:
URL: https://github.com/apache/spark/pull/31772#issuecomment-792344070
**[Test build #135845 has started](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/135845/testReport)** for PR 31772 at commit [`1849fb8`](https://github.com/apache/spark/commit/1849fb812b4be3d2ae63bd649bde3ce220588858).
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[GitHub] [spark] tanelk commented on pull request #31772: [WIP][SPARK-33851][SQL] Push partial aggregate bellow manually inserted repartition
Posted by GitBox <gi...@apache.org>.
tanelk commented on pull request #31772:
URL: https://github.com/apache/spark/pull/31772#issuecomment-792716522
> Why this closed?
There are some test failures and I'm currently not 100% sure on how to fix those. I might reopen it when I get them fixed, but it might take some time.
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