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From "Patrick Kling (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-7001) Allow configuration changes without restarting configured nodes
Date Thu, 14 Oct 2010 18:38:36 GMT
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

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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