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Hadoop / HBase hotspotting / overloading specific nodes

+4 votes
453 views

I am having a problem with Hadoop maxing out drive space on a select few nodes when I am running an HBase job. The scenario is this:

  • The job is a data import using Map/Reduce / HBase
  • The data is being imported to one table
  • The table only has a couple of regions
  • As the job runs, HBase? / Hadoop? begins placing the data in HDFS on the datanode / regionserver that is hosting the regions
  • As the job progresses (and more data is imported) the two datanodes hosting the regions start to get full and eventually drive space hits 100% utilization whilst the other nodes in the cluster are at 40% or less drive space utilization
  • The job in Hadoop then begins to hang with multiple "out of space" errors and eventually fails.

I have tried running hadoop balancer during the job run and this helped but only really succeeded in prolonging the eventual job failure.

How can I get Hadoop / HBase to distribute the data to HDFS more evenly when it is favoring the nodes that the regions are on?

Am I missing something here?

posted Oct 9, 2014 by anonymous

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can you set a reserved room for non-dfs usage? Just to avoid the disk gets full.
dfs.datanode.du.reserved
Reserved space in bytes per volume. Always leave this much space free for non dfs use.
commented Oct 9, 2014 by Honey

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int max_sum=0; 
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Here I am writing minimum,maximum and mean of wordcount.

My input file :

high low medium high low high low large small medium

Actual output is :

high - 3------maximum

low - 3--------maximum

large - 1------minimum

small - 1------minimum

but i am not getting above output ...can anyone please help me?

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