GitHub user dongjoon-hyun opened a pull request:
https://github.com/apache/spark/pull/13906
[SPARK-16208][SQL] Add `CollapseEmptyPlan` optimizer
## What changes were proposed in this pull request?
This PR adds a new logical optimizer, `CollapseEmptyPlan`, to collapse a
logical plans consisting of only empty LocalRelations. The only exceptional
logical plan is aggregation. For aggregation plan, only simple cases are
consider for this optimization.
**Before**
```scala
scala> sql("select a from values (1,2) T(a,b) where 1=0 group by a,b having
a>1 order by a,b").explain
== Physical Plan ==
*Project [a#11]
+- *Sort [a#11 ASC, b#12 ASC], true, 0
+- Exchange rangepartitioning(a#11 ASC, b#12 ASC, 200)
+- *HashAggregate(keys=[a#11, b#12], functions=[])
+- Exchange hashpartitioning(a#11, b#12, 200)
+- *HashAggregate(keys=[a#11, b#12], functions=[])
+- LocalTableScan <empty>, [a#11, b#12]
```
**After**
```scala
scala> sql("select a from values (1,2) T(a,b) where 1=0 group by a,b having
a>1 order by a,b").explain
== Physical Plan ==
LocalTableScan <empty>, [a#0]
```
## How was this patch tested?
Pass the Jenkins tests (including a new testsuite).
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/dongjoon-hyun/spark SPARK-16208
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/13906.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 #13906
----
commit 7ddf449d39f22090bc8aa157fae12c79ba00928e
Author: Dongjoon Hyun <dongj...@apache.org>
Date: 2016-06-25T09:18:44Z
[SPARK-16208][SQL] Add `CollapseEmptyPlan` optimizer
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