Apache Nutch：FetcherJob在Gora中引发NoSuchElementException

Question

我开箱即用运行Apache Nutch 2.3.1，它使用Gora
0.6.1。我已按照此处的说明进行操作：http :
//wiki.apache.org/nutch/RunNutchInEclipse

与InjectorJob。很好。

现在，我正在运行FetcherJob，而Gora MemStore用作数据存储。我gora.properties包含

gora.datastore.default=org.apache.gora.memory.store.MemStore

这引发：

2016-10-02 22:55:54,605 ERROR mapreduce.GoraRecordReader (GoraRecordReader.java:nextKeyValue(121)) - Error reading Gora records: null
2016-10-02 22:55:54,605 INFO  mapred.MapTask (MapTask.java:flush(1460)) - Starting flush of map output
2016-10-02 22:55:54,614 INFO  mapred.LocalJobRunner (LocalJobRunner.java:runTasks(456)) - map task executor complete.
2016-10-02 22:55:54,615 WARN  mapred.LocalJobRunner (LocalJobRunner.java:run(560)) - job_local874667143_0001
java.lang.Exception: java.lang.RuntimeException: java.util.NoSuchElementException
    at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
    at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:522)
Caused by: java.lang.RuntimeException: java.util.NoSuchElementException
    at org.apache.gora.mapreduce.GoraRecordReader.nextKeyValue(GoraRecordReader.java:122)
    at org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.nextKeyValue(MapTask.java:556)
    at org.apache.hadoop.mapreduce.task.MapContextImpl.nextKeyValue(MapContextImpl.java:80)
    at org.apache.hadoop.mapreduce.lib.map.WrappedMapper$Context.nextKeyValue(WrappedMapper.java:91)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:145)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:787)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
    at org.apache.hadoop.mapred.LocalJobRunner$Job$MapTaskRunnable.run(LocalJobRunner.java:243)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.util.NoSuchElementException
    at java.util.concurrent.ConcurrentSkipListMap.firstKey(ConcurrentSkipListMap.java:2036)
    at org.apache.gora.memory.store.MemStore.execute(MemStore.java:128)
    at org.apache.gora.query.impl.QueryBase.execute(QueryBase.java:73)
    at org.apache.gora.mapreduce.GoraRecordReader.executeQuery(GoraRecordReader.java:67)
    at org.apache.gora.mapreduce.GoraRecordReader.nextKeyValue(GoraRecordReader.java:109)
    ... 12 more
2016-10-02 22:55:55,383 INFO  mapreduce.Job (Job.java:monitorAndPrintJob(1360)) - Job job_local874667143_0001 running in uber mode : false
2016-10-02 22:55:55,385 INFO  mapreduce.Job (Job.java:monitorAndPrintJob(1367)) -  map 0% reduce 0%
2016-10-02 22:55:55,387 INFO  mapreduce.Job (Job.java:monitorAndPrintJob(1380)) - Job job_local874667143_0001 failed with state FAILED due to: NA
2016-10-02 22:55:55,396 INFO  mapreduce.Job (Job.java:monitorAndPrintJob(1385)) - Counters: 0
Exception in thread "main" java.lang.RuntimeException: job failed: name=, jobid=job_local874667143_0001
    at org.apache.nutch.util.NutchJob.waitForCompletion(NutchJob.java:119)
    at org.apache.nutch.fetcher.FetcherJob.run(FetcherJob.java:205)
    at org.apache.nutch.fetcher.FetcherJob.fetch(FetcherJob.java:251)
    at org.apache.nutch.fetcher.FetcherJob.run(FetcherJob.java:314)
    at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
    at org.apache.nutch.fetcher.FetcherJob.main(FetcherJob.java:321)

这种情况发生在Nutch和Gora的深处，我不知道为什么会这样。我尝试升级到Gora
0.8，但存在相同的问题。我尝试将Gora降级到0.6，同样的问题。我想切换到hBase之类的其他数据存储，但这对我目前的需求来说有点过头了。

请帮我解决这个问题。

Answer 1

我确认问题出在MemStore。

在0.6.1中存在一个错误：https :
//github.com/apache/gora/blob/apache-gora-0.6.1/gora-
core/src/main/java/org/apache/gora/memory/store
/MemStore.java#L128

这已经在master中解决：https :
//github.com/apache/gora/blob/master/gora-
core/src/main/java/org/apache/gora/memory/store/MemStore.java#L155，对#firstKey（）的访问具有保护#isEmpty（）

但是，不要尝试更新到Gora 0.7-SNAPSHOT，因为Nutch到目前为止尚未适应它。

编辑

如果您想在Nutch 2.x中使用Gora-0.7-SNAPSHOT，也许您可​​以这样做：

1. 下载版本为0.7-SNAPSHOT的Gora主分支
2. 不要mvn install在山/安装它在Maven的本地仓库
3. 将此补丁应用到Nutch：https : //paste.apache.org/jjqz，以便Nutch 2.3.1将与Gora 0.7-SNAPSHOT一起使用
4. 做Nutch的教学资料

我希望它能起作用:)

编辑2

关于使用HBase，进行本地安装非常容易。

1. 如Nutch2Tutorial中所述，下载HBase 0.98.8-hadoop2
2. 在目录中添加tar.gz文件，例如： /home/you/hbase
3. cd /home/you/hbase/bin
4. ./start-hbase.sh

现在，您可以启动并运行HBase。配置Nutch：

ivy / ivy.xml：查看@Emmanuel关于HBase的ivy依赖项配置的评论。

gora.properties：

gora.datastore.default=org.apache.gora.hbase.store.HBaseStore
gora.datastore.autocreateschema=true
gora.datastore.scanner.caching=100

nutch-site.xml：

<configuration>
<property>
 <name>storage.data.store.class</name>
 <value>org.apache.gora.hbase.store.HBaseStore</value>
 <description>Default class for storing data</description>
</property>
</configuration>

做完了 它将采用HBase的所有默认配置：localhost，/ tmp / …，blablabla