GitHub user maropu opened a pull request:
https://github.com/apache/spark/pull/15980
[SPARK-18528][SQL] Fix a bug to initialise an iterator of aggregation
buffer
## What changes were proposed in this pull request?
This pr is to fix an `NullPointerException` issue caused by a following
`limit + aggregate` query;
```
scala> val df = Seq(("a", 1), ("b", 2), ("c", 1), ("d", 5)).toDF("id",
"value")
scala> df.limit(2).groupBy("id").count().show
WARN TaskSetManager: Lost task 0.0 in stage 9.0 (TID 8204,
lvsp20hdn012.stubprod.com): java.lang.NullPointerException
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIterator.agg_doAggregateWithKeys$(Unknown
Source)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIterator.processNext(Unknown
Source)
```
The root culprit is that
[`$doAgg()`](https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala#L596)
skips an initialization of [the buffer
iterator](https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala#L603);
`BaseLimitExec` sets `stopEarly=true` and `$doAgg()` exits in the middle
without the initialization.
## How was this patch tested?
Added a test to check if no exception happens for limit + aggregates in
`DataFrameAggregateSuite.scala`.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/maropu/spark SPARK-18528
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15980.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 #15980
----
commit 31cf318358365fcd237fd9a9ec4f3125996f7e3e
Author: Takeshi YAMAMURO <linguin....@gmail.com>
Date: 2016-11-22T19:18:22Z
Fix a bug to skip the init of hashmap
----
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