Hadoop常见错误及解决办法(2)

同步Hadoop 代码
hadoop-env.sh
# host:path where hadoop code should be rsync'd from. Unset by default.
# export HADOOP_MASTER=master:/home/$USER/src/hadoop

用命令合并HDFS小文件
hadoop fs -getmerge <src> <dest>

重启reduce job方法
Introduced recovery of jobs when JobTracker restarts. This facility is off by default.
Introduced config parameters "mapred.jobtracker.restart.recover", "mapred.jobtracker.job.history.block.size", and "mapred.jobtracker.job.history.buffer.size".
还未验证过。

IO写操作出现问题
0-1246359584298, infoPort=50075, ipcPort=50020):Got exception while serving blk_-5911099437886836280_1292 to /172.16.100.165:
java.net.SocketTimeoutException: 480000 millis timeout while waiting for channel to be ready for write. ch : java.nio.channels.SocketChannel[connected local=/
172.16.100.165:50010 remote=/172.16.100.165:50930]
at org.apache.hadoop.net.SocketIOWithTimeout.waitForIO(SocketIOWithTimeout.java:185)
at org.apache.hadoop.net.SocketOutputStream.waitForWritable(SocketOutputStream.java:159)
at org.apache.hadoop.net.SocketOutputStream.transferToFully(SocketOutputStream.java:198)
at org.apache.hadoop.hdfs.server.datanode.BlockSender.sendChunks(BlockSender.java:293)
at org.apache.hadoop.hdfs.server.datanode.BlockSender.sendBlock(BlockSender.java:387)
at org.apache.hadoop.hdfs.server.datanode.DataXceiver.readBlock(DataXceiver.java:179)
at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:94)
at java.lang.Thread.run(Thread.java:619)

It seems there are many reasons that it can timeout, the example given in
HADOOP-3831 is a slow reading client.

解决办法:在hadoop-site.xml中设置dfs.datanode.socket.write.timeout=0试试;
My understanding is that this issue should be fixed in Hadoop 0.19.1 so that
we should leave the standard timeout. However until then this can help
resolve issues like the one you're seeing.

HDFS退服节点的方法
目前版本的dfsadmin的帮助信息是没写清楚的,已经file了一个bug了,正确的方法如下:
1. 将 dfs.hosts 置为当前的 slaves,文件名用完整路径,注意,列表中的节点主机名要用大名,即 uname -n 可以得到的那个。
2. 将 slaves 中要被退服的节点的全名列表放在另一个文件里,如 slaves.ex,使用 dfs.host.exclude 参数指向这个文件的完整路径
3. 运行命令 bin/hadoop dfsadmin -refreshNodes
4. web界面或 bin/hadoop dfsadmin -report 可以看到退服节点的状态是 Decomission in progress,直到需要复制的数据复制完成为止
5. 完成之后,从 slaves 里(指 dfs.hosts 指向的文件)去掉已经退服的节点

附带说一下 -refreshNodes 命令的另外三种用途:
2. 添加允许的节点到列表中(添加主机名到 dfs.hosts 里来)
3. 直接去掉节点,不做数据副本备份(在 dfs.hosts 里去掉主机名)
4. 退服的逆操作——停止 exclude 里面和 dfs.hosts 里面都有的,正在进行 decomission 的节点的退服,也就是把 Decomission in progress 的节点重新变为 Normal (在 web 界面叫 in service)

hadoop 学习借鉴
1. 解决hadoop OutOfMemoryError问题:
<property>
<name>mapred.child.java.opts</name>
<value>-Xmx800M -server</value>
</property>
With the right JVM size in your hadoop-site.xml , you will have to copy this
to all mapred nodes and restart the cluster.
或者:hadoop jar jarfile [main class] -D mapred.child.java.opts=-Xmx800M

2. Hadoop java.io.IOException: Job failed! at org.apache.hadoop.mapred.JobClient.runJob(JobClient.java:1232) while indexing.
when i use nutch1.0,get this error:
Hadoop java.io.IOException: Job failed! at org.apache.hadoop.mapred.JobClient.runJob(JobClient.java:1232) while indexing.
这个也很好解决:
可以删除conf/log4j.properties,然后可以看到详细的错误报告
我这儿出现的是out of memory
解决办法是在给运行主类org.apache.nutch.crawl.Crawl加上参数:-Xms64m -Xmx512m
你的或许不是这个问题,但是能看到详细的错误报告问题就好解决了

distribute cache使用
类似一个全局变量,但是由于这个变量较大,所以不能设置在config文件中,转而使用distribute cache
具体使用方法:(详见《the definitive guide》,P240)
1. 在命令行调用时:调用-files,引入需要查询的文件(可以是local file, HDFS file(使用hdfs://xxx?)), 或者 -archives (JAR,ZIP, tar等)
% hadoop jar job.jar MaxTemperatureByStationNameUsingDistributedCacheFile \
-files input/ncdc/metadata/stations-fixed-width.txt input/ncdc/all output
2. 程序中调用:
public void configure(JobConf conf) {
metadata = new NcdcStationMetadata();
try {
metadata.initialize(new File("stations-fixed-width.txt"));
} catch (IOException e) {
throw new RuntimeException(e);
}
}
另外一种间接的使用方法:在hadoop-0.19.0中好像没有
调用addCacheFile()或者addCacheArchive()添加文件,
使用getLocalCacheFiles() 或 getLocalCacheArchives() 获得文件

hadoop的job显示web
There are web-based interfaces to both the JobTracker (MapReduce master) and NameNode (HDFS master) which display status pages about the state of the entire system. By default, these are located at [WWW] :50030/ and [WWW] :50070/.

hadoop监控
OnlyXP(52388483) 131702
用nagios作告警,ganglia作监控图表即可

status of 255 error
错误类型:
java.io.IOException: Task process exit with nonzero status of 255.
at org.apache.hadoop.mapred.TaskRunner.run(TaskRunner.java:424)

错误原因:
Set mapred.jobtracker.retirejob.interval and mapred.userlog.retain.hours to higher value. By default, their values are 24 hours. These might be the reason for failure, though I'm not sure

split size
FileInputFormat input splits: (详见 《the definitive guide》P190)
mapred.min.split.size: default=1, the smallest valide size in bytes for a file split.
mapred.max.split.size: default=Long.MAX_VALUE, the largest valid size.
dfs.block.size: default = 64M, 系统中设置为128M。
如果设置 minimum split size > block size, 会增加块的数量。(猜想从其他节点拿去数据的时候,会合并block,导致block数量增多)
如果设置maximum split size < block size, 会进一步拆分block。

split size = max(minimumSize, min(maximumSize, blockSize));
其中 minimumSize < blockSize < maximumSize.

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