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From "Patrick Kling (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-7001) Allow configuration changes without restarting configured nodes
Date Mon, 25 Oct 2010 21:18:27 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.patch

Here is a new version of my patch. I have changed the interface Reconfigurable somewhat: Since
only a subset of configuration properties can be changed at run time, it makes more sense
to have an interface that allows us to change a single property at a time, rather than passing
a Configuration object and then detecting all changes that need to be made. I have also added
methods for detecting which configuration properties can be changed at runtime.

 * Something whose {@link Configuration} can be changed at run time.                     
public interface Reconfigurable extends Configurable {

   * Change a the configuration property on this object to the value specified.          
   * Change a the configuration property on this object to the value specified           
   * and return the previous value that the configuration property was set to            
   * (or null if it was not previously set).                                             
   * If the property cannot be changed, throw a                                          
   * {@link ConfigurationChangeException}.                                               
  public String changeConfProperty(String property, String newVal)
    throws ConfigurationChangeException;

   * Return whether a given property is changeable at run time.                          
   * If isConfPropertyChangeable returns true for a property,                            
   * then changeConf should not throw an exception when changing                         
   * this property.                                                                      
  public boolean isConfPropertyChangeable(String property);

   * Return all the properties that can be changed at run time.                          
  public List<String> getChangeableConfProperties();

The patch also includes a simple servlet for changing the configuration of a Reconfigurable.
In order to allow configuration changes at run time, I made all the getters and setters in
Configuration synchronized.

> 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.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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