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BELUGA BEHR edited comment on HDFS-14292 at 2/20/19 4:52 PM: ------------------------------------------------------------- [~xkrogen] Thanks for the feedback. Well, I don't know the history, but I too seemed thought it was the obvious choice, but I will tell you that it's not easy to do... unit tests are failing and I haven't pinned it down quite yet (ugh), but I think some of the code is expecting that threads are not-reused via ThreadLocal and other mechanisms. I'm still trying to hunt it down exactly, but the unit tests pass when I use a thread pool that does not re-use threads. was (Author: belugabehr): [~xkrogen] Thanks for the feedback. Well, I don't know the history, but I too seemed like it was the obvious choice, but I will tell you that it's not easy to do... unit tests are failing and I haven't pinned it down quite yet (ugh), but I think some of the code is expecting that threads are not-reused via ThreadLocal and other mechanisms. I'm still trying to hunt it down exactly, but the unit tests pass when I use a thread pool that does not re-use threads. > Introduce Java ExecutorService to DataXceiverServer > --------------------------------------------------- > > Key: HDFS-14292 > URL: https://issues.apache.org/jira/browse/HDFS-14292 > Project: Hadoop HDFS > Issue Type: Improvement > Components: datanode > Affects Versions: 3.2.0 > Reporter: BELUGA BEHR > Assignee: BELUGA BEHR > Priority: Major > Attachments: HDFS-14292.1.patch, HDFS-14292.2.patch, > HDFS-14292.3.patch > > > I wanted to investigate {{dfs.datanode.max.transfer.threads}} from > {{hdfs-site.xml}}. It is described as "Specifies the maximum number of > threads to use for transferring data in and out of the DN." The default > value is 4096. I found it interesting because 4096 threads sounds like a lot > to me. I'm not sure how a system with 8-16 cores would react to this large a > thread count. Intuitively, I would say that the overhead of context > switching would be immense. > During mt investigation, I discovered the > [following|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataXceiverServer.java#L203-L216] > setup in the {{DataXceiverServer}} class: > # A peer connects to a DataNode > # A new thread is spun up to service this connection > # The thread runs to completion > # The tread dies > It would perhaps be better if we used a thread pool to better manage the > lifecycle of the service threads and to allow the DataNode to re-use existing > threads, saving on the need to create and spin-up threads on demand. > In this JIRA, I have added a couple of things: > # Added a thread pool to {{DataXceiverServer}} class that, on demand, will > create up to {{dfs.datanode.max.transfer.threads}}. A thread that has > completed its prior duties will stay idle for up to 60 seconds > (configurable), it will be retired if no new work has arrived. > # Added new methods to the {{Peer}} Interface to allow for better logging and > less code within each Thread ({{DataXceiver}}). > # Updated the Thread code ({{DataXceiver}}) regarding its interactions with > {{blockReceiver}} instance variable -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org