[GitHub] [hadoop] goiri commented on a change in pull request #1755: HDFS-15047. Document the new decommission monitor (HDFS-14854).

[GitBox <gi...@apache.org>]

goiri commented on a change in pull request #1755: HDFS-15047. Document the new decommission monitor (HDFS-14854).
URL: https://github.com/apache/hadoop/pull/1755#discussion_r356783677
 
 

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 File path: hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsDataNodeAdminGuide.md
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 @@ -148,6 +148,35 @@ dfs.namenode.decommission.blocks.per.interval
 dfs.namenode.decommission.max.concurrent.tracked.nodes
 ```
 
+
+Backing-off Decommission Monitor (experimental)
+------------
+
+Original decommissioning algorithm has issues when DataNodes having lots of
+blocks are decommissioned such as
+
+* Write lock in the NameNode could be held for a long time for queueing re-replication.
+* Re-replication work progresses node by node if there are multiple decommissioning DataNodes.
+
+[HDFS-14854](https://issues.apache.org/jira/browse/HDFS-14854) introduced
+new decommission monitor in order to migigates those issues.
+This feature is currently marked as experimental and disabled by default.
+You can enable this by setting the value of
+`dfs.namenode.decommission.monitor.class` to
+`org.apache.hadoop.hdfs.server.blockmanagement.DatanodeAdminBackoffMonitor`
+in hdfs-site.xml.
+
+Relevant configuration properties are listed in the table below.
 
 Review comment:
   "*The* relevant"

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