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https://issues.apache.org/jira/browse/HADOOP-4061?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12650304#action_12650304
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Raghu Angadi commented on HADOOP-4061:
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I think there is too much code that is not really required. probably
complicating it much more than required.
- Storing reference should be be fine. This is java.. we should just check if
the DN is already deleted.
- Alternately, the monitor can in each iteration :
--- list all the decommissioned nodes and
--- the just pick five of them randomly to check.
just a suggestion.
> 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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