我是Hadoop的新手，并尝试使用Hadoop编写关联连接。该算法试图在两个连续轮次中加入三个关系。我使用递归方法。该计划工作正常。但在执行期间，它会尝试打印这样的警告：
14/12/02 10:41:16 WARN io.ReadaheadPool: Failed readahead on ifile
EBADF: Bad file descriptor
at org.apache.hadoop.io.nativeio.NativeIO$POSIX.posix_fadvise(Native Method)
at org.apache.hadoop.io.nativeio.NativeIO$POSIX.posixFadviseIfPossible(NativeIO.java:263)
at org.apache.hadoop.io.nativeio.NativeIO$POSIX$CacheManipulator.posixFadviseIfPossible(NativeIO.java:142)
at org.apache.hadoop.io.ReadaheadPool$ReadaheadRequestImpl.run(ReadaheadPool.java:206)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
这很烦人，我想知道问题的原因以及如何摆脱它们。我的代码如下：
public class Recursive {
/**
* Join three relations together using recursive method
* R JOIN S JOIN T = ((R JOIN S) JOIN T)
*/
static String[] relationSequence; // Keeps sequence of relations in join
static int round; // Round number running
/**
* Mapper
* Relation name = R
* Input tuple = a b
* Output pair = (b, (R,a))
* We assume that join value is the last attribute for the first relation
* and the first attribute for the second relation.
* So using this assumption, this map-reduce algorithm will work for any number of attributes
*/
public static class joinMapper extends Mapper<Object, Text, IntWritable, Text>{
public void map(Object keyIn, Text valueIn, Context context) throws IOException, InterruptedException {
// Read tuple and put attributes in a string array
String curValue = valueIn.toString();
String[] values = curValue.split("\t");
// Get relation name from input file name
String fileName = ((FileSplit) context.getInputSplit()).getPath().getName();
// Get join attribute index number R join S
int joinIndex;
String others = "";
if(fileName.compareTo(relationSequence[round])==0){
joinIndex = 0;
others = curValue.substring(0+2);
}else{
joinIndex = values.length - 1;
others = curValue.substring(0, curValue.length()-2);
}
IntWritable joinValue = new IntWritable(Integer.parseInt(values[joinIndex]));
// Create list of attributes which are not join attribute
Text temp = new Text(fileName + "|" + others);
context.write(joinValue,temp);
}
}
/**
* Reducer
*
* 1. Divide the input list in two ArrayLists based on relation name:
* a. first relation
* b. second relation
* 2. Test if the second relation is not empty. If it's so, we shouldn't continue.
* 3. For each element of the first array list, join it with the all elements in
* the second array list
*/
public static class joinReducer extends Reducer<IntWritable, Text, Text, Text>{
public void reduce(IntWritable keyIn, Iterable<Text> valueIn, Context context)
throws IOException, InterruptedException{
ArrayList<String> firstRelation = new ArrayList<String>();
ArrayList<String> secondRelation = new ArrayList<String>();
for (Text value : valueIn) {
String[] values = value.toString().split("\\|");
if(values[0].compareTo(relationSequence[round])==0){
secondRelation.add(values[1]);
}else{
firstRelation.add(values[1]);
}
}
if(secondRelation.size()>0){
for (String firstItem : firstRelation) {
for (String secondItem : secondRelation) {
context.write(new Text(firstItem.toString()), new Text(keyIn.toString() + "\t"
+ secondItem.toString()
));
}
}
}
}
}
/**
* Partitioner
*
* In order to hash pairs to reducer tasks, we used logical which is
* obviously faster than module function.
*/
public static class joinPartitioner extends Partitioner<IntWritable, Text> {
public int getPartition(IntWritable key, Text value, int numReduceTasks) {
int partitionNumber = key.get()&0x007F;
return partitionNumber;
}
}
/**
* Main method
*
* (R join S join T)
* hadoop jar ~/COMP6521.jar Recursive /input/R /input/S /input2/T /output R,S,T
*
* @param args
* <br> args[0]: first relation
* <br> args[1]: second relation
* <br> args[2]: third relation
* <br> args[3]: output directory
* <br> args[4]: relation sequence to join, separated by comma
*/
public static void main(String[] args) throws IllegalArgumentException, IOException, InterruptedException, ClassNotFoundException {
long s = System.currentTimeMillis();
/****** Preparing problem variables *******/
relationSequence = args[4].split(","); // Keep sequence of relations
round = 1; // Variable to keep current round number
int maxOfReducers = 128; // Maximum number of available reducers
int noReducers; // Number of reducers for one particular job
noReducers = maxOfReducers;
Path firstRelation = new Path(args[0]);
Path secondRelation = new Path(args[1]);
Path thirdRelation = new Path(args[2]);
Path temp = new Path("/temp"); // Temporary path to keep intermediate result
Path out = new Path(args[3]);
/****** End of variable Preparing *******/
Configuration conf = new Configuration();
/****** Configuring first job *******/
// General configuration
Job job = Job.getInstance(conf, "Recursive multi-way join (first round)");
job.setNumReduceTasks(noReducers);
// Pass appropriate classes
job.setJarByClass(Recursive.class);
job.setMapperClass(joinMapper.class);
job.setPartitionerClass(joinPartitioner.class);
job.setReducerClass(joinReducer.class);
// Specify input and output type of reducers
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
job.setMapOutputKeyClass(IntWritable.class);
job.setMapOutputValueClass(Text.class);
FileSystem fs = FileSystem.get(conf);
if(fs.exists(temp)){ fs.delete(temp, true);}
if(fs.exists(out)) { fs.delete(out, true); }
// Specify the input and output paths
FileInputFormat.addInputPath(job, firstRelation);
FileInputFormat.addInputPath(job, secondRelation);
FileOutputFormat.setOutputPath(job, temp);
/****** End of first job configuration *******/
job.submit();
// Running the first job
boolean b = job.waitForCompletion(true);
if(b){
// try to execute the second job after completion of the first one
round++; // Specify round number
Configuration conf2 = new Configuration(); // Create new configuration object
/****** Configuring second job *******/
// General configuration
Job job2 = Job.getInstance(conf2, "Reduce multi-way join (second round)");
job2.setNumReduceTasks(noReducers);
// Pass appropriate classes
job2.setJarByClass(Recursive.class);
job2.setMapperClass(joinMapper.class);
job2.setPartitionerClass(joinPartitioner.class);
job2.setReducerClass(joinReducer.class);
// Specify input and output type of reducers
job2.setOutputKeyClass(Text.class);
job2.setOutputValueClass(Text.class);
// Specify input and output type of mappers
job2.setMapOutputKeyClass(IntWritable.class);
job2.setMapOutputValueClass(Text.class);
// End of 2014-11-25
// Specify the input and output paths
FileInputFormat.addInputPath(job2, temp);
FileInputFormat.addInputPath(job2, thirdRelation);
FileOutputFormat.setOutputPath(job2, out);
/****** End of second job configuration *******/
job2.submit();
// Running the first job
b = job2.waitForCompletion(true);
// Output time measurement
long e = System.currentTimeMillis() - s;
System.out.println("Total: " + e);
System.exit(b ? 0 : 1);
}
System.exit(1);
}
}
答案 0 :(得分：4)
我遇到了类似的错误，我最终会回答您的问题，而mail list thread EBADF: Bad file descriptor
为了澄清一下，预读池有时会吐出来 如果您在预读请求处于运行状态时关闭文件，则会显示该消息。它的 不是错误，只是反映了文件匆忙关闭的事实， 可能是因为其他一些错误是真正的问题。
在我的情况下，我关闭了一位作家而没有使用hflush
由于你似乎没有手工使用作家或读者，我可能会看看你如何发送先生任务。