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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6808) Add command line option to ask DataNode reload configuration.
Date Fri, 19 Sep 2014 15:50:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6808?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14140765#comment-14140765

Allen Wittenauer commented on HDFS-6808:

bq. The client doesn't have the list of all datanodes.

Actually, it might through dfs.hosts.  This sounds like a very reasonable thing to do.  If
no hostname is provided, it should process dfs.hosts and dfs.hosts.exclude and use the remaining

bq. How about assuming the default DataNode IPC port if the port is left off? 

Sounds like a good option.

bq. The client reading its XML file is even worse. There's absolutely no guarantee that its
XML file is the same as the one that the datanode is using.

>From a software experience perspective, Hadoop commands have always processed the local
XML file to grab options, whether the authors of that code was aware of it or not.  This is
one of the ways in which overrides happen.   It's more than reasonable to use the local XML
file as a basis of this information; it's expected behavior at this point.  

bq. I think you are underestimating our support folks. They're pretty aware of the various
kinds of refresh operations that we support and what problems each command had / still has,
sometimes more so than I am. Reconfig is a new operation. It is its own thing, not related
to anything else. That's why I asked Eddy to rename references to "decommissioning drives"
in the original patch. This isnt' a decom operation, nor is it a refresh operation.

Just the opposite, actually.  There is more than enough evidence for me to know that you rarely
read what I write seriously, so I'm hoping they can convince you that in operations refresh/reload/reconfig
are all synonyms of each other.  It just depends upon which group built what software. Users
who aren't neck deep into the code day-in, day-out *will* confuse these verbs.

> Add command line option to ask DataNode reload configuration.
> -------------------------------------------------------------
>                 Key: HDFS-6808
>                 URL: https://issues.apache.org/jira/browse/HDFS-6808
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode
>    Affects Versions: 2.5.0
>            Reporter: Lei (Eddy) Xu
>            Assignee: Lei (Eddy) Xu
>         Attachments: HDFS-6808.000.combo.patch, HDFS-6808.000.patch, HDFS-6808.001.combo.patch,
HDFS-6808.001.patch, HDFS-6808.002.combo.patch, HDFS-6808.002.patch, HDFS-6808.003.combo.txt,
HDFS-6808.003.patch, HDFS-6808.004.combo.patch, HDFS-6808.004.patch, HDFS-6808.005.combo.patch,
HDFS-6808.005.patch, HDFS-6808.006.combo.patch, HDFS-6808.006.patch, HDFS-6808.007.combo.patch,
HDFS-6808.007.patch, HDFS-6808.008.combo.patch, HDFS-6808.008.patch, HDFS-6808.009.combo.patch,
HDFS-6808.009.patch, HDFS-6808.010.patch
> The workflow of dynamically changing data volumes on DataNode is
> # Users manually changed {{dfs.datanode.data.dir}} in the configuration file
> # User use command line to notify DN to reload configuration and updates its volumes.

> This work adds command line support to notify DN to reload configuration.

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