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https://issues.apache.org/jira/browse/HDFS-14295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16779937#comment-16779937
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BELUGA BEHR commented on HDFS-14295:
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[~elgoiri] Unfortunately, we cannot. The running threads depend on (interact
with) some of these other services, so we need to wait for these threads to
complete (max 30s) before closing down the other services. There are going to
be a lot of race conditions if these threads are running while the rest of the
services are being closed.
This may be worth its own JIRA: To ensure that all of the components are being
shutdown in a proper order.
> 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, HDFS-14295.4.patch, HDFS-14295.5.patch,
> HDFS-14295.6.patch, HDFS-14295.7.patch, HDFS-14295.8.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.
> 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.
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