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https://issues.apache.org/jira/browse/HADOOP-7001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921584#action_12921584
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Patrick Kling commented on HADOOP-7001:
---------------------------------------
I have uploaded a patch with the changes proposed in this JIRA. The included
base class can be used to easily implement the interface by overriding the
method changeProperty, which modifies a single configuration property:
{code}
/**
* Change a property or throw an exception.
*
* Subclasses should overrride this.
* If newVal is null, change the property to its default value.
*/
protected boolean changeProperty(String property, String newVal)
throws ConfigurationChangeException {
throw new ConfigurationChangeException(property, newVal,
getConf().get(property));
}
{code}
This should enable us to include whatever code is necessary to make a
configuration change. The overridden version of this method should also serve
as a good documentation of what changes are supported by a particular class.
Below is a version of the Reconfigurable interface with more detailed comments.
Unfortunately, I cannot edit my previous comments, so I apologize if this is
somewhat redundant:
{code}
package org.apache.hadoop.conf;
/**
* Something whose {...@link Configuration} can be changed at run time.
*/
public interface Reconfigurable extends Configurable {
/**
* Change the configuration of this object.
*
* Change the configuration of this object to the configuration
* passed as conf.
* If it is not possible to change a configuration option,
* a {...@link ConfigurationChangeException} is thrown
* and no changes are made to the current configuration.
*
* Detailed semantics:
* * If a property is set in the current configuration and in newConf, then
* the configuration must be updated to reflect the value in newConf.
* * If a property is not set in the current configuration but is set in
* newConf, then the configuration must be set to the value in newConf.
* * If a property is set in the current configuration but is not set in
* newConf, then the configuration must revert to the default value for
* this property.
* * If the change required by these rules is not possible, a
* ConfigurationChangeException must be thrown.
*/
void changeConf(Configuration newConf) throws ConfigurationChangeException;
}
{code}
> 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: 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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