Predictionio评估失败，出现Empty.maxBy异常，并使用java.lang.OutOfMemoryError进行训练

我已经下载了文本分类模板的最新更新。我创建了一个新应用，并通过指定应用ID导入了stopwords.json和emails.json

$ pio import --appid <appID> --input data/stopwords.json
$ pio import --appid <appID> --input data/emails.json

然后，我更改了engine.json并在其中指定了我的应用名称。

{
   "id": "default",
   "description": "Default settings",
   "engineFactory":   "org.template.textclassification.TextClassificationEngine",
   "datasource": {
   "params": {
   "appName": "<myapp>",
   "evalK": 3
}

但是下一步，即评估失败，并显示错误empty.maxBy。错误的一部分粘贴在下面

[INFO] [Engine$] Preparator:  org.template.textclassification.Preparator@79a13920
[INFO] [Engine$] AlgorithmList: List(org.template.textclassification.LRAlgorithm@420a8042)
[INFO] [Engine$] Serving: org.template.textclassification.Serving@faea4da
Exception in thread "main" java.lang.UnsupportedOperationException:  empty.maxBy
at scala.collection.TraversableOnce$class.maxBy(TraversableOnce.scala:223)
at scala.collection.AbstractTraversable.maxBy(Traversable.scala:105)
at org.template.textclassification.PreparedData.<init> (Preparator.scala:160)
at org.template.textclassification.Preparator.prepare(Preparator.scala:39)
at org.template.textclassification.Preparator.prepare(Preparator.scala:35)
at io.prediction.controller.PPreparator.prepareBase(PPreparator.scala:34)
at io.prediction.controller.Engine$$anonfun$25.apply(Engine.scala:758)
at scala.collection.MapLike$MappedValues.get(MapLike.scala:249)
at scala.collection.MapLike$MappedValues.get(MapLike.scala:249)
at scala.collection.MapLike$class.apply(MapLike.scala:140)
at scala.collection.AbstractMap.apply(Map.scala:58)

然后我尝试了，pio train但是在显示一些观察结果之后，训练也失败了。显示的错误为java.lang.OutOfMemoryError: Java heap space。错误的一部分粘贴在下面。

[INFO] [Engine$] Data santiy check is on.
[INFO] [Engine$] org.template.textclassification.TrainingData supports data sanity check. Performing check.

Observation 1 label: 1.0
Observation 2 label: 0.0
Observation 3 label: 0.0
Observation 4 label: 1.0
Observation 5 label: 1.0

[INFO] [Engine$] org.template.textclassification.PreparedData does not support data sanity check. Skipping check.
[WARN] [BLAS] Failed to load implementation from: com.github.fommil.netlib.NativeSystemBLAS
[WARN] [BLAS] Failed to load implementation from: com.github.fommil.netlib.NativeRefBLAS
[INFO] [Engine$] org.template.textclassification.NBModel does not support data sanity check. Skipping check.
[INFO] [Engine$] EngineWorkflow.train completed
[INFO] [Engine] engineInstanceId=AU3g4XyhTrUUakX3xepP
[INFO] [CoreWorkflow$] Inserting persistent model
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:3236)
at java.io.ByteArrayOutputStream.grow(ByteArrayOutputStream.java:118)
at  java.io.ByteArrayOutputStream.ensureCapacity(ByteArrayOutputStream.java:93)
at java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:153)
at com.esotericsoftware.kryo.io.Output.flush(Output.java:155)
at com.twitter.chill.Tuple2Serializer.write(TupleSerializers.scala:36)
at com.twitter.chill.Tuple2Serializer.write(TupleSerializers.scala:33)
at com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:568)
at  com.twitter.chill.TraversableSerializer$$anonfun$write$1.apply(Traversable.scala:29)

这是因为内存不足吗？我运行的同一模板的先前版本的文本分类数据大于40mb，没有问题。评估是否必须进行培训？还可以请您解释一下评估是如何进行的吗？