GitHub user scwf opened a pull request:
https://github.com/apache/spark/pull/5821
[SPARK-7289] [SQL] CombineLimits improvement: push down sort when it's
child is Limit
Optimize following sql
`select key from (select * from testData limit 5) t order by key limit 5`
before this PR:
```
== Parsed Logical Plan ==
'Limit 5
'Sort ['key ASC], true
'Project ['key]
'Subquery t
'Limit 5
'Project [*]
'UnresolvedRelation [testData], None
== Analyzed Logical Plan ==
Limit 5
Sort [key#0 ASC], true
Project [key#0]
Subquery t
Limit 5
Project [key#0,value#1]
Subquery testData
LogicalRDD [key#0,value#1], MapPartitionsRDD[1]
== Optimized Logical Plan ==
Limit 5
Sort [key#0 ASC], true
Project [key#0]
Limit 5
LogicalRDD [key#0,value#1], MapPartitionsRDD[1]
== Physical Plan ==
TakeOrdered 5, [key#0 ASC]
Project [key#0]
Limit 5
PhysicalRDD [key#0,value#1], MapPartitionsRDD[1]
```
after this PR
```
== Parsed Logical Plan ==
'Limit 5
'Sort ['key ASC], true
'Project ['key]
'Subquery t
'Limit 5
'Project [*]
'UnresolvedRelation [testData], None
== Analyzed Logical Plan ==
Limit 5
Sort [key#0 ASC], true
Project [key#0]
Subquery t
Limit 5
Project [key#0,value#1]
Subquery testData
LogicalRDD [key#0,value#1], MapPartitionsRDD[1]
== Optimized Logical Plan ==
Limit 5
Sort [key#0 ASC], true
Project [key#0]
LogicalRDD [key#0,value#1], MapPartitionsRDD[1]
== Physical Plan ==
TakeOrdered 5, [key#0 ASC]
Project [key#0]
PhysicalRDD [key#0,value#1], MapPartitionsRDD[1]
```
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/scwf/spark limit
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/5821.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 #5821
----
commit 494cc25eb9b51b1333e5ba95082be6568e17ee20
Author: scwf <[email protected]>
Date: 2015-04-30T23:23:39Z
push down sort when it's child is Limit
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