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https://issues.apache.org/jira/browse/HDFS-14854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16956552#comment-16956552
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Wei-Chiu Chuang commented on HDFS-14854:
----------------------------------------
Thanks [~sodonnell]
I finally gave it a hard look at the patch. The patch looks reasonable to me.
But a patch this big will inevitably introduce bugs in corner cases or race
condition bugs. Next step would be to set up a small cluster, generate a few
million files and shake out easy bugs.
There's a minor conflict because of HDFS-14847.
There's a typo:
{code}
LOG.error("P{ is set to an invalid value, it must be greater than "+
"zero. Defaulting to {}",
{code}
I think you wanted instead
{code}
LOG.error("{} is set to an invalid value, it must be greater than "+
"zero. Defaulting to {}",
{code}
> 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, HDFS-14854.010.patch,
> HDFS-14854.011.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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