I assume you are on Linux. Also assuming that your tasks are so resource intensive that they are taking down nodes. You should enable limits per task, see http://hadoop.apache.org/docs/stable/cluster_setup.html#Memory+monitoring
What it does is that jobs are now forced to up front provide their resource requirements, and TTs enforce those limits.
+Vinod Kumar Vavilapalli
On Sep 16, 2013, at 1:35 PM, Forrest Aldrich wrote:
> We recently experienced a couple of situations that brought one or more Hadoop nodes down (unresponsive). One was related to a bug in a utility we use (ffmpeg) that was resolved by compiling a new version. The next, today, occurred after attempting to join a new node to the cluster.
> A basic start of the (local) tasktracker and datanode did not work -- so based on reference, I issued: hadoop mradmin -refreshNodes, which was to be followed by hadoop dfsadmin -refreshNodes. The load average literally jumped to 60 and the master (which also runs a slave) became unresponsive.
> Seems to me that this should never happen. But, looking around, I saw an article from Spotify which mentioned the need to set certain resource limits on the JVM as well as in the system itself (limits.conf, we run RHEL). I (and we) are fairly new to Hadoop, so some of these issues are very new.
> I wonder if some of the experts here might be able to comment on this issue - perhaps point out settings and other measures we can take to prevent this sort of incident in the future.
> Our setup is not complicated. Have 3 hadoop nodes, the first is also a master and a slave (has more resources, too). The underlying system we do is split up tasks to ffmpeg (which is another issue as it tends to eat resources, but so far with a recompile, we are good). We have two more hardware nodes to add shortly.
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