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[GitHub] [spark] ulysses-you opened a new pull request, #37330: [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression
ulysses-you opened a new pull request, #37330:
URL: https://github.com/apache/spark/pull/37330
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### What changes were proposed in this pull request?
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Optimize Global sort to RepartitionByExpression, for example:
```
Sort local Sort local
Sort global => RepartitionByExpression
```
### Why are the changes needed?
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If a global sort below a local sort, the only meaningful thing is it's distribution. So this pr optimizes that global sort to RepartitionByExpression to save a local sort.
### Does this PR introduce _any_ user-facing change?
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no, only improve performance
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add test
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[GitHub] [spark] cloud-fan closed pull request #37330: [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression
Posted by GitBox <gi...@apache.org>.
cloud-fan closed pull request #37330: [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression
URL: https://github.com/apache/spark/pull/37330
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "maytasm (via GitHub)" <gi...@apache.org>.
maytasm commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1868219583
@cloud-fan Confirmed that PR https://github.com/apache/spark/pull/44429 fixed the issue I was having with the no-op sort!
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1837693411
hi @maytasm , `Sort global` is semantics equal to `Sort local + RepartitionByExpression`. For your case, if there is only single value on the sort column, then Sort global would also introduce a range partitioning shuffle and make a single partition task at the end. Can you show a real case if you find any behavior change ?
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[GitHub] [spark] cloud-fan commented on pull request #37330: [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1199430528
cc @sigmod
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1867413757
Oh now I get it. This is sort by a constant. Can you try the latest master branch? I think https://github.com/apache/spark/pull/44429/files#diff-11264d807efa58054cca2d220aae8fba644ee0f0f2a4722c46d52828394846efR214 has solved it.
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "maytasm (via GitHub)" <gi...@apache.org>.
maytasm commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1867341537
@ulysses-you
Sorry for the late reply. That is true unless the following condition is True for the `Sort global`:
` case s @ Sort(orders, _, child) if orders.isEmpty || orders.exists(_.child.foldable) =>
val newOrders = orders.filterNot(_.child.foldable)
if (newOrders.isEmpty) {
applyLocally.lift(child).getOrElse(child)
}
`
In the case that the above condition is True, then this `Sort global` will be removed. However, with this change (in this PR), the `Sort global` will not be removed as it would have been turn into a RepartitionByExpression
Consider the following case:
`
+- Sort [date#0 ASC NULLS FIRST], false
+- Project [...]
+- Sort [20231221 ASC NULLS FIRST], true
+- Aggregate [...]
+- RelationV2[...] some_table
`
with the change from this PR, the `Sort [20231221 ASC NULLS FIRST], true` would be remove. We would end up with
`
+- Sort [date#0 ASC NULLS FIRST], false
+- Project [...]
+- Aggregate [...]
+- RelationV2[...] some_table
`
However, with the change in this PR:
`
+- Sort [date#0 ASC NULLS FIRST], false
+- Project [...]
+- Exchange rangepartition (20231221 ASC NULL FIRST)
+- Aggregate [...]
+- RelationV2[...] some_table
`
The problem here is that `Exchange rangepartition` reduces the partition to 1. Then the stages after that like the Sort on date#0 ran with a single task.
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1867347895
> without the change from this PR, the Sort [20231221 ASC NULLS FIRST], true would be remove.
Are you sure? It looks wrong to do so
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[GitHub] [spark] cloud-fan commented on pull request #37330: [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1201979396
@ulysses-you can you open a backport PR for 3.3? I think this is a necessary followup of https://github.com/apache/spark/pull/37250 to avoid perf regression.
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "maytasm (via GitHub)" <gi...@apache.org>.
maytasm commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1867364494
@cloud-fan
Can you expand on why you think the `Sort [20231221 ASC NULLS FIRST], true` looks wrong to remove? It is a sort that has no reference and should be fine to remove.
`Sort [20231221 ASC NULLS FIRST], true` would look something like:
Since Literal is foldable, `newOrders` would be empty. As `newOrders` is empty, the sort is then removed.
This is explained in https://github.com/apache/spark/pull/11840
I believe this PR prevents the optimization added in https://github.com/apache/spark/pull/11840 to work as intended since it convert the no-op sort into RepartitionByExpression, which can no longer be removed
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[GitHub] [spark] cloud-fan commented on pull request #37330: [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1200744193
thanks, merging to master!
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "maytasm (via GitHub)" <gi...@apache.org>.
maytasm commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1836761095
@ulysses-you @cloud-fan
Not sure if I am missing something but can this causes performance degradation if my sort order is on a key with few/single values?
For example, if I have 500 shuffle partitions...
Without this change:
```
Sort local
Sort global
```
both of the above stages would run with 500 tasks
With this change: and say the RepartitionByExpression is on the column date and there is only a single value for this in my dataset
```
Sort local
RepartitionByExpression
```
RepartitionByExpression will run with 500 tasks and create a single partition
then the Sort would run with a single task (as there is only a single partition)
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Re: [PR] [SPARK-39911][SQL] Optimize global Sort to RepartitionByExpression [spark]
Posted by "maytasm (via GitHub)" <gi...@apache.org>.
maytasm commented on PR #37330:
URL: https://github.com/apache/spark/pull/37330#issuecomment-1867510631
Ah! I haven't tried running yet but took a look at PR https://github.com/apache/spark/pull/44429/ and I think it does solve this issue. So basically the logic for converting `global sort` to `Exchange rangepartition` is moved into another rule, RemoveRedundantSorts, and EliminateSorts is run before RemoveRedundantSorts. Meaning the no-op sort like `Sort [20231221 ASC NULLS FIRST], true` would be remove by EliminateSorts already by the time RemoveRedundantSorts is run.
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