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Posted to hdfs-issues@hadoop.apache.org by "David Mollitor (Jira)" <ji...@apache.org> on 2019/08/29 18:14:00 UTC
[jira] [Commented] (HDFS-13157) Do Not Remove Blocks Sequentially
During Decommission
[ https://issues.apache.org/jira/browse/HDFS-13157?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16918836#comment-16918836 ]
David Mollitor commented on HDFS-13157:
---------------------------------------
I need to validate that blocks are actually being deleted in order, but it's likely.
Note to self:
Consider doing the shuffle here:
https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeDescriptor.java#L729-L730
> Do Not Remove Blocks Sequentially During Decommission
> ------------------------------------------------------
>
> Key: HDFS-13157
> URL: https://issues.apache.org/jira/browse/HDFS-13157
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode, namenode
> Affects Versions: 3.0.0
> Reporter: David Mollitor
> Priority: Major
>
> From what I understand of [DataNode decommissioning|https://github.com/apache/hadoop/blob/42a1c98597e6dba2e371510a6b2b6b1fb94e4090/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeAdminManager.java] it appears that all the blocks are scheduled for removal _in order._. I'm not 100% sure what the ordering is exactly, but I think it loops through each data volume and schedules each block to be replicated elsewhere. The net affect is that during a decommission, all of the DataNode transfer threads slam on a single volume until it is cleaned out. At which point, they all slam on the next volume, etc.
> Please randomize the block list so that there is a more even distribution across all volumes when decommissioning a node.
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