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https://issues.apache.org/jira/browse/HDFS-14295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16771385#comment-16771385
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BELUGA BEHR edited comment on HDFS-14295 at 2/18/19 9:25 PM:
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Also note that this means that some of these threads are being counted in the
MXBean, so you could see cases where the MXBean reported a number higher than
{{dfs.datanode.max.transfer.thread}} which is a bit confusing.
[Check it out
here|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java#L2197-L2201]
was (Author: belugabehr):
Also note that this means that some of these threads are being counted in the
MXBean, so you could see cases where the MXBean reported a number higher than
{{dfs.datanode.max.transfer.thread}} which is a bit confusing.
[Here|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java#L2197-L2201]
> Add Threadpool for DataTransfers
> --------------------------------
>
> Key: HDFS-14295
> URL: https://issues.apache.org/jira/browse/HDFS-14295
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 3.2.0
> Reporter: BELUGA BEHR
> Assignee: BELUGA BEHR
> Priority: Major
> Attachments: HDFS-14295.1.patch, HDFS-14295.2.patch,
> HDFS-14295.3.patch
>
>
> When a DataNode data transfers a block, is spins up a new thread for each
> transfer.
> [Here|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java#L2339]
> and
> [Here|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java#L3019-L3022].
> Instead, add the threads to a {{CachedThreadPool}} so that when their
> threads complete the transfer, they can be re-used for another transfer. This
> should save resources spent on creating and spinning up transfer threads.
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