GitHub user maropu opened a pull request:
https://github.com/apache/spark/pull/11997
[SPARK-14193][SQL] Skip unnecessary sorts if input data have been already
ordered in InMemoryRelation
## What changes were proposed in this pull request?
This pr is to skip unnecessary sorts if input data have been already
ordered in InMemoryRelation.
Let's say we have a cached table with column 'a' sorted;
```
val df1 = Seq((1, 0), (3, 0), (2, 0), (1, 0)).toDF("a", "b")
val df2 = df1.sort("a").cache
df2.show // just cache data
```
If you say `df2.sort("a")`, the current spark generates a plan like;
```
== Physical Plan ==
Sort [a#13 ASC], true, 0
+- InMemoryColumnarTableScan [a#13,b#14], InMemoryRelation [a#13,b#14],
true, 10000, StorageLevel(true, true, false, true, 1), Sort [a#13 ASC], true,
0, None
```
This pr removes this unnecessary sort.
## How was this patch tested?
Add tests to check this kind of sort operators is removed in an optimizer.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/maropu/spark SortAttr
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/11997.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #11997
----
commit a035564be6a11566149e7a121e46843dcb826bfc
Author: Takeshi YAMAMURO <[email protected]>
Date: 2016-03-28T09:41:19Z
Skip unnecessary sorts if input data have been already ordered
----
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