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From "Patrick Kling (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-7001) Allow configuration changes without restarting configured nodes
Date Tue, 02 Nov 2010 03:45:28 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-7001?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Patrick Kling updated HADOOP-7001:

    Attachment: HADOOP-7001.3.patch

Here is an updated patch. Navigating to the ReconfigurationServlet for a Reconfigurable node
now reloads the configuration files from disk and shows a list of all properties that have
changed (along with their old and new values). If there are any changes to properties that
cannot be reconfigured at run time, a warning is shown. After reviewing the changes, the admin
can approve them, at which point they are applied through the methods in the Reconfigurable

The code for computing the diff between the old and the new configuration is in ReconfigurationUtil,
which should make it easy to add this functionality to existing command line tools.

For this revision, I didn't end up going with the PropertyChangeListener API, since there
doesn't seem to be an ideal source object with which to register listeners while still keeping
this change generic enough to be useful for all configured nodes in the system.

The review board revision corresponding to this patch can be found at: https://reviews.apache.org/r/21/

> 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-7001.3.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 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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