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From "Haohui Mai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9000) Allow reconfiguration without restart for parameters where applicable.
Date Tue, 29 Sep 2015 21:06:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9000?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14935852#comment-14935852

Haohui Mai commented on HDFS-9000:

This leads to a much more general discussion -- have you considered making rebooting the NN
/ DN significantly faster instead of making them reconfigurable?

My biggest concern is that whether the approach is a solid direction given the complexity
of NN / DN. There're around ~700 configurations for NN and DN today. A lot of questions need
to be answered given the scale of the configuration. For example, what are parts of the configurations
that are reconfigurable, what are the parts that require a full restart? What happens if failures
happen during the process of reconfiguration? What happens if a daemon ended up in an inconsistent
state? Is it even possible to detect the daemon is in a inconsistent state?

It looks to me that it is much more robust to make restarting much faster (e.g., persisting
information like block reports in DN / NN) instead of making the daemons reconfigurable.

> Allow reconfiguration without restart for parameters where applicable.
> ----------------------------------------------------------------------
>                 Key: HDFS-9000
>                 URL: https://issues.apache.org/jira/browse/HDFS-9000
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 2.7.0
>            Reporter: Xiaobing Zhou
>            Assignee: Xiaobing Zhou
> Many parameters can be re-configured without requiring a restart.

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