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https://issues.apache.org/jira/browse/HDFS-14295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16771376#comment-16771376
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BELUGA BEHR commented on HDFS-14295:
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One thing I'll point out that's a bit off, which I address in this patch, ...
There are two places in the code where a {{DataTransfer}} thread is started. In
[one
place|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java#L2339-L2341],
it's started in a default thread group. In [another
place|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],
it's started in the
[dataXceiverServer|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java#L1164]
thread group.
I do not think it's correct to include any of these threads in the
{{dataXceiverServer}} thread group. Anything submitted to the
{{dataXceiverServer}} should probably be tied to the
{{dfs.datanode.max.transfer.threads}} configurations, and neither of these
methods are. Instead, they should be submitted into the same thread pool with
its own thread group (probably the default thread group, unless someone
suggests otherwise) and is what I have included in this patch.
> 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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