如何解决此错误org.apache.spark.sql.catalyst.errors.package $ TreeNodeException

Question

我有两个过程，每个过程都要做1）连接oracle db读取特定表2）形成数据框并对其进行处理。3）将df保存到cassandra。

如果我同时运行两个进程，则两者都尝试从oracle读取，而第二个进程读取数据时却出现错误提示

 ERROR ValsProcessor2: org.apache.spark.sql.catalyst.errors.package$TreeNodeException: execute, tree:
Exchange SinglePartition
+- *(1) HashAggregate(keys=[], functions=[partial_count(1)], output=[count#290L])
   +- *(1) Scan JDBCRelation((SELECT * FROM BM_VALS WHERE ROWNUM <= 10) T) [numPartitions=2] [] PushedFilters: [], ReadSchema: struct<>
at org.apache.spark.sql.catalyst.errors.package$.attachTree(package.scala:56)
at org.apache.spark.sql.execution.exchange.ShuffleExchangeExec.doExecute(ShuffleExchangeExec.scala:119)
at org.apache.spark.sql.execution.SparkPlan$$anonfun$execute$1.apply(SparkPlan.scala:131)
at org.apache.spark.sql.execution.SparkPlan$$anonfun$execute$1.apply(SparkPlan.scala:127)
at org.apache.spark.sql.execution.SparkPlan$$anonfun$executeQuery$1.apply(SparkPlan.scala:155)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:151)
at org.apache.spark.sql.execution.SparkPlan.executeQuery(SparkPlan.scala:152)
at org.apache.spark.sql.execution.SparkPlan.execute(SparkPlan.scala:127)
at org.apache.spark.sql.execution.InputAdapter.inputRDDs(WholeStageCodegenExec.scala:371)
at org.apache.spark.sql.execution.aggregate.HashAggregateExec.inputRDDs(HashAggregateExec.scala:150)
at org.apache.spark.sql.execution.WholeStageCodegenExec.doExecute(WholeStageCodegenExec.scala:605)
at org.apache.spark.sql.execution.SparkPlan$$anonfun$execute$1.apply(SparkPlan.scala:131)
at org.apache.spark.sql.execution.SparkPlan$$anonfun$execute$1.apply(SparkPlan.scala:127)
at org.apache.spark.sql.execution.SparkPlan$$anonfun$executeQuery$1.apply(SparkPlan.scala:155)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:151)
at org.apache.spark.sql.execution.SparkPlan.executeQuery(SparkPlan.scala:152)
at org.apache.spark.sql.execution.SparkPlan.execute(SparkPlan.scala:127)
at org.apache.spark.sql.execution.SparkPlan.getByteArrayRdd(SparkPlan.scala:247)
at org.apache.spark.sql.execution.SparkPlan.executeCollect(SparkPlan.scala:294)
at org.apache.spark.sql.Dataset$$anonfun$count$1.apply(Dataset.scala:2770)
at org.apache.spark.sql.Dataset$$anonfun$count$1.apply(Dataset.scala:2769)
at org.apache.spark.sql.Dataset$$anonfun$52.apply(Dataset.scala:3254)
at org.apache.spark.sql.execution.SQLExecution$.withNewExecutionId(SQLExecution.scala:77)
at org.apache.spark.sql.Dataset.withAction(Dataset.scala:3253)
at org.apache.spark.sql.Dataset.count(Dataset.scala:2769)
at com.snp.processors.BenchmarkModelValsProcessor2.process(BenchmarkModelValsProcessor2.scala:43)
at com.snp.utils.Utils$$anonfun$getAllDefinedProcessors$2.apply(Utils.scala:28)
at com.snp.utils.Utils$$anonfun$getAllDefinedProcessors$2.apply(Utils.scala:28)
at com.sp.MigrationDriver$$anonfun$main$2$$anonfun$apply$1.apply(MigrationDriver.scala:78)
at com.sp.MigrationDriver$$anonfun$main$2$$anonfun$apply$1.apply(MigrationDriver.scala:78)
at scala.Option.map(Option.scala:146)
at com.sp.MigrationDriver$$anonfun$main$2.apply(MigrationDriver.scala:75)
at com.sp.MigrationDriver$$anonfun$main$2.apply(MigrationDriver.scala:74)
at scala.collection.Iterator$class.foreach(Iterator.scala:891)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1334)
at scala.collection.MapLike$DefaultKeySet.foreach(MapLike.scala:174)
at com.sp.MigrationDriver$.main(MigrationDriver.scala:74)
at com.sp.MigrationDriver.main(MigrationDriver.scala)
Caused by: java.lang.NullPointerException
    at org.apache.spark.sql.execution.exchange.ShuffleExchangeExec$.needToCopyObjectsBeforeShuffle(ShuffleExchangeExec.scala:163)
    at org.apache.spark.sql.execution.exchange.ShuffleExchangeExec$.prepareShuffleDependency(ShuffleExchangeExec.scala:300)
    at org.apache.spark.sql.execution.exchange.ShuffleExchangeExec.prepareShuffleDependency(ShuffleExchangeExec.scala:91)
    at org.apache.spark.sql.execution.exchange.ShuffleExchangeExec$$anonfun$doExecute$1.apply(ShuffleExchangeExec.scala:128)
    at org.apache.spark.sql.execution.exchange.ShuffleExchangeExec$$anonfun$doExecute$1.apply(ShuffleExchangeExec.scala:119)
    at org.apache.spark.sql.catalyst.errors.package$.attachTree(package.scala:52)
    ... 37 more

我在这里做错了什么？如何解决呢？

Answer 1

我不确定真正的原因，唯一引起我注意的是下面的 SQL 表达式：(SELECT * FROM BM_VALS WHERE ROWNUM <= 10) T-T这里的意思是什么？

关于整体设计，我会推荐完全不同的方法。在您的情况下，您有 2 个处理器处理从 Oracle 收集的相同数据，并且每个处理器单独获取数据。我建议将 Oracle 数据的读取转移到单独的过程中，该过程将返回数据帧（您需要缓存它），然后您的处理器将处理该数据帧并将数据保存到 Cassandra 中。

或者正如之前建议的那样，您可以将作业分成两部分 - 一个从 Oracle 中提取所有数据，并将数据帧存储到磁盘中（不是persist，而是使用write），例如作为 Parquet 文件。然后分离将从磁盘获取数据的作业，并执行必要的转换。

在这两种情况下你