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https://issues.apache.org/jira/browse/HADOOP-16656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16957628#comment-16957628
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Siyao Meng commented on HADOOP-16656:
-------------------------------------
[~dineshchitlangia] Thanks for the comment.
Yes, in the most typical usage of FairCallQueue, {{[port_number]}} should be
set to the NN RPC port (in {{dfs.namenode.rpc-address}}). But I don't really
see anything preventing users from setting {{[port_number]}} to NN service RPC
port (in dfs.namenode.servicerpc-address) or lifeline port (in
{{dfs.namenode.lifeline.rpc-address}}).
So I tested (trunk) locally with 1 NN and 1 DN,
(1) {{[port_number]}} can be set to NN RPC port (in
{{dfs.namenode.rpc-address}}) *without* setting a NN service RPC address/port
({{dfs.namenode.servicerpc-address}});
(2) {{[port_number]}} can be set to NN service RPC port (in
{{dfs.namenode.servicerpc-address}});
(3) {{[port_number]}} can be set to NN lifeline RPC port (in
{{dfs.namenode.lifeline.rpc-address}});
In all 3 cases above, I can start NN and DN, and successfully run a shell
command "{{hdfs dfs -ls /}}" with the NN.
One explanation is that, even if {{ipc.[port_number].callqueue.impl}} is *not*
set, it defaults to {{LinkedBlockingQueue}}, as shown in the code
[here|https://github.com/apache/hadoop/blob/1654497f98fb7f2de8214d2fbad305b7a2854816/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/Server.java#L691].
So in theory, {{[port_number]}} could be set to any RPC port opened on NN.
I haven't dug into FairCallQueue implementation in its entirety - there might
be some other exceptions I didn't realize.
Instead, we could remind users that they typically want to set
{{[port_number]}} to NN RPC port rather than the other two (NN service RPC
port, or lifeline port)?
> Document FairCallQueue configs in core-default.xml
> --------------------------------------------------
>
> Key: HADOOP-16656
> URL: https://issues.apache.org/jira/browse/HADOOP-16656
> Project: Hadoop Common
> Issue Type: Task
> Reporter: Siyao Meng
> Assignee: Siyao Meng
> Priority: Major
> Attachments: HADOOP-16656.001.patch
>
>
> So far those callqueue / scheduler / faircallqueue -related configurations
> are only documented in FairCallQueue.md in 3.3.0:
> https://aajisaka.github.io/hadoop-document/hadoop-project/hadoop-project-dist/hadoop-common/FairCallQueue.html#Full_List_of_Configurations
> (Thanks Akira for uploading this.)
> Goal: Document those configs in core-default.xml as well to make it easier
> for users(admins) to find and use.
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