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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-7001) Allow configuration changes without restarting configured nodes
Date Tue, 26 Oct 2010 04:11:24 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12924832#action_12924832
] 

Todd Lipcon commented on HADOOP-7001:
-------------------------------------

I'm not sold on the interface being one of "set conf var 'foo' to value 'bar'". Internally,
this seems fine, but exposing this as a servlet seems like it will encourage the case where
runtime configuration diverges from what's in the XML configuration files on disk.

Could we instead have the servlet/API be more similar to the existing refresh* functions,
where it reloads the configuration off disk, and applies a diff? I'm imagining the servlet
would show you a "preview" of the diff to be applied, along with a list of warnings for configuration
variables that have been changed on disk but are *not* reconfigurable. Then the administrator
can hit an "apply" button to reconfigure the settings that are reconfigurable.

> Allow configuration changes without restarting configured nodes
> ---------------------------------------------------------------
>
>                 Key: HADOOP-7001
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7001
>             Project: Hadoop Common
>          Issue Type: Task
>            Reporter: Patrick Kling
>            Assignee: Patrick Kling
>         Attachments: HADOOP-7001.2.patch, HADOOP-7001.patch, reconfigurable.patch
>
>
> Currently, changing the configuration on a node (e.g., the name node) requires that we
restart the node. We propose a change that would allow us to make configuration changes without
restarting. Nodes that support configuration changes at run time should implement the following
interface:
> interface ChangeableConfigured extends Configured {
>    void changeConfiguration(Configuration newConf) throws ConfigurationChangeException;
> }
> The contract of changeConfiguration is as follows:
> The node will compare newConf to the existing configuration. For each configuration property
that is set to a different value than in the current configuration, the node will either adjust
its behaviour to conform to the new configuration or throw a ConfigurationChangeException
if this change is not possible at run time. If a configuration property is set in the current
configuration but is unset in newConf, the node should use its default value for this property.
After a successful invocation of changeConfiguration, the behaviour of the configured node
should be indistinguishable from the behaviour of a node that was configured with newConf
at creation.
> It should be easy to change existing nodes to implement this interface. We can start
by throwing the exception for all changes and then gradually start supporting more and more
changes at run time. (We might even consider replacing Configured with ChangeableConfigured
entirely, but I think the proposal above afford greater flexibility).

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