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From "Koji Noguchi (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-4061) Large number of decommission freezes the Namenode
Date Wed, 03 Sep 2008 18:05:44 GMT
Large number of decommission freezes the Namenode

                 Key: HADOOP-4061
                 URL: https://issues.apache.org/jira/browse/HADOOP-4061
             Project: Hadoop Core
          Issue Type: Bug
          Components: dfs
    Affects Versions: 0.17.2
            Reporter: Koji Noguchi

On 1900 nodes cluster, we tried decommissioning 400 nodes with 30k blocks each. Other 1500
nodes were almost empty.

When decommission started, namenode's queue overflowed every 6 minutes.

Looking at the cpu usage,  it showed that every 5 minutes org.apache.hadoop.dfs.FSNamesystem$DecommissionedMonitor
thread was taking 100% of the CPU for 1 minute causing the queue to overflow.

  public synchronized void decommissionedDatanodeCheck() {
    for (Iterator<DatanodeDescriptor> it = datanodeMap.values().iterator();
         it.hasNext();) {
      DatanodeDescriptor node = it.next();

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