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https://issues.apache.org/jira/browse/HADOOP-4061?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12650338#action_12650338
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Suresh Srinivas commented on HADOOP-4061:
-----------------------------------------
Minor nits:
In CyclicIterable.java, navigablemap != null check not required:
{noformat}
hasnext = navigablemap != null && !next.equals(first);
{noformat}
In DecommissionManager.java, move setting the firstkey in to the return
condition.
{noformat}
+ if (++count == numNodesPerCheck) {
>> add here firstkey = entry.getKey();
+ return;
+ }
{noformat}
> 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
> Assignee: Tsz Wo (Nicholas), SZE
> Attachments: 4061_20081119.patch, 4061_20081120.patch,
> 4061_20081120b.patch, 4061_20081123.patch, 4061_20081124.patch
>
>
> 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.
> {noformat}
> public synchronized void decommissionedDatanodeCheck() {
> for (Iterator<DatanodeDescriptor> it = datanodeMap.values().iterator();
> it.hasNext();) {
> DatanodeDescriptor node = it.next();
> checkDecommissionStateInternal(node);
> }
> }
> {noformat}
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