beliefer opened a new pull request, #37977:
URL: https://github.com/apache/spark/pull/37977
### What changes were proposed in this pull request?
When `AggregatingAccumulator` serialize aggregate buffer, may throwing NPE.
There is one test case could repeat this error.
```
val namedObservation = Observation("named")
val df = spark.range(1, 10, 1, 10)
val observed_df = df.observe(
namedObservation, percentile_approx($"id", lit(0.5),
lit(100)).as("percentile_approx_val"))
observed_df.collect()
```
throws exception as follows:
```
13:45:10.976 ERROR org.apache.spark.util.Utils: Exception encountered
java.lang.NullPointerException
at
org.apache.spark.sql.catalyst.expressions.aggregate.TypedImperativeAggregate.getBufferObject(interfaces.scala:641)
at
org.apache.spark.sql.catalyst.expressions.aggregate.TypedImperativeAggregate.getBufferObject(interfaces.scala:602)
at
org.apache.spark.sql.catalyst.expressions.aggregate.TypedImperativeAggregate.serializeAggregateBufferInPlace(interfaces.scala:624)
at
org.apache.spark.sql.execution.AggregatingAccumulator.withBufferSerialized(AggregatingAccumulator.scala:205)
at
org.apache.spark.sql.execution.AggregatingAccumulator.withBufferSerialized(AggregatingAccumulator.scala:33)
at
org.apache.spark.util.AccumulatorV2.writeReplace(AccumulatorV2.scala:186)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at
java.io.ObjectStreamClass.invokeWriteReplace(ObjectStreamClass.java:1245)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1136)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at
org.apache.spark.scheduler.DirectTaskResult.$anonfun$writeExternal$2(TaskResult.scala:55)
at
org.apache.spark.scheduler.DirectTaskResult.$anonfun$writeExternal$2$adapted(TaskResult.scala:55)
at scala.collection.Iterator.foreach(Iterator.scala:943)
at scala.collection.Iterator.foreach$(Iterator.scala:943)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1431)
at scala.collection.IterableLike.foreach(IterableLike.scala:74)
at scala.collection.IterableLike.foreach$(IterableLike.scala:73)
at scala.collection.AbstractIterable.foreach(Iterable.scala:56)
at
org.apache.spark.scheduler.DirectTaskResult.$anonfun$writeExternal$1(TaskResult.scala:55)
at
scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
at org.apache.spark.util.Utils$.tryOrIOException(Utils.scala:1456)
at
org.apache.spark.scheduler.DirectTaskResult.writeExternal(TaskResult.scala:51)
at
java.io.ObjectOutputStream.writeExternalData(ObjectOutputStream.java:1459)
at
java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1430)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at
org.apache.spark.serializer.JavaSerializationStream.writeObject(JavaSerializer.scala:46)
at
org.apache.spark.serializer.JavaSerializerInstance.serialize(JavaSerializer.scala:115)
at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:663)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
```
### Why are the changes needed?
Fix a bug.
After my investigation, The root cause is the buffer of
`AggregatingAccumulator` will not be created if the input rows is empty.
### Does this PR introduce _any_ user-facing change?
'Yes'.
Users will see the correct results.
### How was this patch tested?
New test case.
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