空RDD上的转换结果 [英] Result of transformation on an Empty RDD

问题描述

我有一个RDD（combinerRDD），我在这个RDD下应用了转换

  JavaPairRDD< String，Integer> count = combinerRDD.mapToPair（
）新PairFunction< Tuple2< LongWritable，Text>，String，Integer>（）{
字符串文件名; 
整数; 
消息; 
 
 @Override 
 public Tuple2< String，Integer> call（Tuple2< LongWritable，Text> tuple）throws Exception {
 xlhrCount = 0; 
 filename =; 
 
 filename =New_File; 
 for（JobStep js：message.getJobStep（））{
 if（js.getStepName（）。equals（StepName.NEW_STEP））{
 count + = 1; 
} 
} 
 
返回新的Tuple2< String，Integer>（filename，xlhrCount）; 
} 
} ）.reduceByKey（新函数2<整数，整数，整数> （）{
 @Override 
 public Integer调用（Integer count1，Integer count2）抛出Exception {
 return（count1 + count2）; 
} 
} 
）; 
  

我的问题是当 combinerRDD 有一些数据在里面，我得到了正确的结果。但是当 combinerRDD 为空时，写入HDFS的结果只是一个空的_SUCCESS文件。我期待2个文件在空RDD上转换，例如_SUCCESS和空白部分00000文件。我对吗？我应该得到多少个输出文件。

我之所以问这是因为我在2个群集中得到了不同的结果，群集1上运行的代码导致了_SUCCESS文件并且第2组导致了_SUCCESS和空的部分00000。我现在很困惑。注意：我在 newRDD.leftOuterJoin（combinerRDD）上进行左连接是否依赖任何群集设置？

c>，这给了我没有结果（当combinerRDD只有_SUCCESS）和newRDD包含值时。

解决方案

一个办法。我正在使用spark-1.3.0，它有以下问题：ie。一个emptyRDD的左外连接会给出空结果。

https://issues.apache.org/jira/browse/SPARK-9236

我创建了如下所示的空对RDD ：

  JavaRDD< Tuple2< LongWritable，Text>> emptyRDD = context.emptyRDD（）; 
 myRDD = JavaPairRDD.fromJavaRDD（emptyRDD）; 
  

现在使用：

 列表< Tuple2< LongWritable，Text>> data = Arrays.asList（）; 
 JavaRDD< Tuple2< LongWritable，Text>> emptyRDD = context.parallelize（data）; 
 myRDD = JavaPairRDD.fromJavaRDD（emptyRDD）; 
  

它现在可以工作，即我的RDD不再是空的。修正版本有以下版本：
1.3.2,1.4.2,1.5.0（参考上面的链接）。

I have an RDD(combinerRDD)on which I applied below transformation

    JavaPairRDD<String, Integer> counts = combinerRDD.mapToPair(
            new PairFunction<Tuple2<LongWritable, Text>, String, Integer>() {
                String filename;
                Integer count;
                Message message;

                @Override
                public Tuple2<String, Integer> call(Tuple2<LongWritable, Text> tuple) throws Exception {
                    xlhrCount = 0;
                    filename = "";

                        filename = "New_File";
                        for (JobStep js : message.getJobStep()) {
                            if (js.getStepName().equals(StepName.NEW_STEP)) {
                                count += 1;
                            }
                        }

                    return new Tuple2<String, Integer>(filename, xlhrCount);
                }
            }).reduceByKey(new Function2<Integer, Integer, Integer>() {
                               @Override
                               public Integer call(Integer count1, Integer count2) throws Exception {
                                   return (count1 + count2);
                               }
                           }
    );

My question is when combinerRDD has some data inside, I get right result .But when combinerRDD is empty the result written into HDFS is only an empty _SUCCESS file . I was expecting 2 files in the case of transformation on an empty RDD ie _SUCCESS and empty part-00000 file .Am I right? How many output files should I get .

I reason why I am asking this is because I got different result in 2 clusters , the code ran on cluster 1 resulted in _SUCCESS file and cluster 2 resulted in _SUCCESS and empty part-00000 . I am confused now . Is the result dependent on any cluster setup?

Note : I am doing a left join on newRDD.leftOuterJoin(combinerRDD), which gives me no result(when combinerRDD has only _SUCCESS) and newRDD contains value .

解决方案

Ok,so I found a solution. I am using spark-1.3.0, which has below issue: ie. a left outer join with an emptyRDD gives empty result .

https://issues.apache.org/jira/browse/SPARK-9236

I was creating empty Pair RDD like below:

JavaRDD<Tuple2<LongWritable, Text>> emptyRDD = context.emptyRDD();
myRDD = JavaPairRDD.fromJavaRDD(emptyRDD);

Now using :

List<Tuple2<LongWritable, Text>> data = Arrays.asList();
JavaRDD<Tuple2<LongWritable, Text>> emptyRDD = context.parallelize(data);
myRDD = JavaPairRDD.fromJavaRDD(emptyRDD);

It works now, ie my RDD is no more empty. Fix is available in versions: 1.3.2, 1.4.2, 1.5.0 (reference above link).

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