我正在4核，16 GB Ram的单台计算机上运行Spark 2.3。
我想使用具有用户，项目和等级的ALS来为1GB数据集训练隐式模型。进行等级5，迭代10的训练
我正在使用1个执行程序，2个执行程序内核，12 GB执行程序内存，1个驱动程序节点和1GB驱动程序内存。另外，我将分区数设置为30。甚至将persist（）设置为Disk_Only，以减少内存负载。
我还提到了Checkpoint目录sc.setCheckpointDir（'/ tmp'）。
仍然，我面临着超出GC开销限制的问题。我应该如何解决？
我正在附加错误的堆栈跟踪：
18/11/22 08:03:36 ERROR executor.Executor: Exception in task 0.0 in stage 6.0 (TID 36)
java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.util.Arrays.copyOf(Arrays.java:3332)
at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:596)
at java.lang.StringBuilder.append(StringBuilder.java:190)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFSpan(ObjectInputStream.java:3496)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFBody(ObjectInputStream.java:3404)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:3216)
at java.io.ObjectInputStream.readString(ObjectInputStream.java:1896)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1558)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1561)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
18/11/22 08:03:36 ERROR executor.Executor: Exception in task 1.0 in stage 6.0 (TID 37)
java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.util.Arrays.copyOf(Arrays.java:3332)
at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:596)
at java.lang.StringBuilder.append(StringBuilder.java:190)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFSpan(ObjectInputStream.java:3496)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFBody(ObjectInputStream.java:3404)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:3216)
at java.io.ObjectInputStream.readString(ObjectInputStream.java:1896)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1558)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1561)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
18/11/22 08:03:36 ERROR util.SparkUncaughtExceptionHandler: Uncaught exception in thread Thread[Executor task launch worker for task 37,5,main]
java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.util.Arrays.copyOf(Arrays.java:3332)
at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:596)
at java.lang.StringBuilder.append(StringBuilder.java:190)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFSpan(ObjectInputStream.java:3496)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFBody(ObjectInputStream.java:3404)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:3216)
at java.io.ObjectInputStream.readString(ObjectInputStream.java:1896)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1558)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1561)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
18/11/22 08:03:36 ERROR util.SparkUncaughtExceptionHandler: Uncaught exception in thread Thread[Executor task launch worker for task 36,5,main]
java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.util.Arrays.copyOf(Arrays.java:3332)
at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:596)
at java.lang.StringBuilder.append(StringBuilder.java:190)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFSpan(ObjectInputStream.java:3496)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFBody(ObjectInputStream.java:3404)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:3216)
at java.io.ObjectInputStream.readString(ObjectInputStream.java:1896)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1558)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1561)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
18/11/22 08:03:36 ERROR scheduler.TaskSetManager: Task 0 in stage 6.0 failed 1 times; aborting job
Exception in thread "main" org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 6.0 failed 1 times, most recent failure: Lost task 0.0 in stage 6.0 (TID 36, localhost, executor driver): java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.util.Arrays.copyOf(Arrays.java:3332)
at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:596)
at java.lang.StringBuilder.append(StringBuilder.java:190)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFSpan(ObjectInputStream.java:3496)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFBody(ObjectInputStream.java:3404)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:3216)
at java.io.ObjectInputStream.readString(ObjectInputStream.java:1896)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1558)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1561)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
Driver stacktrace:
at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$failJobAndIndependentStages(DAGScheduler.scala:1599)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1587)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1586)
at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
at org.apache.spark.scheduler.DAGScheduler.abortStage(DAGScheduler.scala:1586)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:831)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:831)
at scala.Option.foreach(Option.scala:257)
at org.apache.spark.scheduler.DAGScheduler.handleTaskSetFailed(DAGScheduler.scala:831)
at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.doOnReceive(DAGScheduler.scala:1820)
at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1769)
at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1758)
at org.apache.spark.util.EventLoop$$anon$1.run(EventLoop.scala:48)
at org.apache.spark.scheduler.DAGScheduler.runJob(DAGScheduler.scala:642)
at org.apache.spark.SparkContext.runJob(SparkContext.scala:2027)
at org.apache.spark.SparkContext.runJob(SparkContext.scala:2048)
at org.apache.spark.SparkContext.runJob(SparkContext.scala:2067)
at org.apache.spark.rdd.RDD$$anonfun$take$1.apply(RDD.scala:1358)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:151)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:112)
at org.apache.spark.rdd.RDD.withScope(RDD.scala:363)
at org.apache.spark.rdd.RDD.take(RDD.scala:1331)
at org.apache.spark.rdd.RDD$$anonfun$isEmpty$1.apply$mcZ$sp(RDD.scala:1466)
at org.apache.spark.rdd.RDD$$anonfun$isEmpty$1.apply(RDD.scala:1466)
at org.apache.spark.rdd.RDD$$anonfun$isEmpty$1.apply(RDD.scala:1466)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:151)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:112)
at org.apache.spark.rdd.RDD.withScope(RDD.scala:363)
at org.apache.spark.rdd.RDD.isEmpty(RDD.scala:1465)
at org.apache.spark.ml.recommendation.ALS$.train(ALS.scala:918)
at org.apache.spark.ml.recommendation.ALS.fit(ALS.scala:674)
at Saavn.Clustering.Test.main(Test.java:93)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.spark.deploy.JavaMainApplication.start(SparkApplication.scala:52)
at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:892)
at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:197)
at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:227)
at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:136)
at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
Caused by: java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.util.Arrays.copyOf(Arrays.java:3332)
at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:596)
at java.lang.StringBuilder.append(StringBuilder.java:190)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFSpan(ObjectInputStream.java:3496)
at java.io.ObjectInputStream$BlockDataInputStream.readUTFBody(ObjectInputStream.java:3404)
at java.io.ObjectInputStream$BlockDataInputStream.readUTF(ObjectInputStream.java:3216)
at java.io.ObjectInputStream.readString(ObjectInputStream.java:1896)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1558)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1561)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567)
at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1966)
[root@ip-172-31-94-232 saavn]#
[root@ip-172-31-94-232 saavn]# spark-shell
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/fs/FSDataInputStream
at org.apache.spark.deploy.SparkSubmitArguments$$anonfun$mergeDefaultSparkProperties$1.apply(SparkSubmitArguments.scala:123)
at org.apache.spark.deploy.SparkSubmitArguments$$anonfun$mergeDefaultSparkProperties$1.apply(SparkSubmitArguments.scala:123)
at scala.Option.getOrElse(Option.scala:120)
at org.apache.spark.deploy.SparkSubmitArguments.mergeDefaultSparkProperties(SparkSubmitArguments.scala:123)
at org.apache.spark.deploy.SparkSubmitArguments.<init>(SparkSubmitArguments.scala:109)
at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:114)
at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.fs.FSDataInputStream
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:338)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 7 more
我已经尝试设置检查点，但是仍然遇到相同的问题。
SC.setCheckpointDir("hdfs:///user/ec2-user/als");
ALS als = new ALS().setRank(5)
.setMaxIter(10)
.setRegParam(0.01)
.setImplicitPrefs(true)
.setUserCol("UserID")
.setItemCol("SongID")
.setRatingCol("SongFreq").setCheckpointInterval(2);