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https://issues.apache.org/jira/browse/HDFS-14854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16952169#comment-16952169
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Hadoop QA commented on HDFS-14854:
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| JIRA Issue | HDFS-14854 |
| JIRA Patch URL | 
https://issues.apache.org/jira/secure/attachment/12983085/HDFS-14854.009.patch |
| Console output | 
https://builds.apache.org/job/PreCommit-HDFS-Build/28091/console |
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> Create improved decommission monitor implementation
> ---------------------------------------------------
>
>                 Key: HDFS-14854
>                 URL: https://issues.apache.org/jira/browse/HDFS-14854
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 3.3.0
>            Reporter: Stephen O'Donnell
>            Assignee: Stephen O'Donnell
>            Priority: Major
>         Attachments: Decommission_Monitor_V2_001.pdf, HDFS-14854.001.patch, 
> HDFS-14854.002.patch, HDFS-14854.003.patch, HDFS-14854.004.patch, 
> HDFS-14854.005.patch, HDFS-14854.006.patch, HDFS-14854.007.patch, 
> HDFS-14854.008.patch, HDFS-14854.009.patch
>
>
> In HDFS-13157, we discovered a series of problems with the current 
> decommission monitor implementation, such as:
>  * Blocks are replicated sequentially disk by disk and node by node, and 
> hence the load is not spread well across the cluster
>  * Adding a node for decommission can cause the namenode write lock to be 
> held for a long time.
>  * Decommissioning nodes floods the replication queue and under replicated 
> blocks from a future node or disk failure may way for a long time before they 
> are replicated.
>  * Blocks pending replication are checked many times under a write lock 
> before they are sufficiently replicate, wasting resources
> In this Jira I propose to create a new implementation of the decommission 
> monitor that resolves these issues. As it will be difficult to prove one 
> implementation is better than another, the new implementation can be enabled 
> or disabled giving the option of the existing implementation or the new one.
> I will attach a pdf with some more details on the design and then a version 1 
> patch shortly.



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