hadoop中日志聚集问题

遇到的问题：

当点击上面的logs时，会出现下面问题：

这个解决方案为：

By default, Hadoop stores the logs of each container in the node where that container was hosted. While this is irrelevant if you're just testing some Hadoop executions in a single-node environment (as all the logs will be in your machine anyway), with a cluster of nodes, keeping track of the logs can become quite a bother. In addition, since logs are kept on the normal filesystem, you may run into storage problems if you keep logs for a long time or have heterogeneous storage capabilities.

Log aggregation is a new feature that allows Hadoop to store the logs of each application in a central directory in HDFS. To activate it, just add the following to yarn-site.xmland restart the Hadoop services:

 <property>
    <description>Whether to enable log aggregation</description>
    <name>yarn.log-aggregation-enable</name>
    <value>true</value>
  </property>

By adding this option, you're telling Hadoop to move the application logs to hdfs:///logs/userlogs/<your user>/<app id>. You can change this path and other options related to log aggregation by specifying some other properties mentioned in the default yarn-site.xml (just do a search for log.aggregation).

However, these aggregated logs are not stored in a human readable format so you can't just cat their contents. Fortunately, Hadoop developers have included several handy command line tools for reading them:

# Read logs from any YARN application
$HADOOP_HOME/bin/yarn logs -applicationId <applicationId>
 
# Read logs from MapReduce jobs
$HADOOP_HOME/bin/mapred job -logs <jobId>
 
# Read it in a scrollable window with search (type '/' followed by your query).
$HADOOP_HOME/bin/yarn logs -applicationId <applicationId> | less
 
# Or just save it to a file and use your favourite editor
$HADOOP_HOME/bin/yarn logs -applicationId <applicationId> > log.txt

You can also access these logs via a web app for MapReduce jobs by using the JobHistory daemon. This daemon can be started/stopped by running the following:

# Start JobHistory daemon
$HADOOP_PREFIX/sbin/mr-jobhistory-daemon.sh start historyserver
# Stop JobHistory daemon
$HADOOP_PREFIX/sbin/mr-jobhistory-daemon.sh stop historyserver

My Fabric script includes an optional variable for setting the node where to launch this daemon so it is automatically started/stopped when you run fab start or fab stop.

Unfortunately, a generic history daemon for universal web access to aggregated logs does not exist yet. However, as you can see by checking YARN-321, there's considerable work being done in this area. When this gets introduced I'll update this section.