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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, 26 Oct 2010 02:32:22 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-7001.2.patch

As suggested by Doug, I have renamed the methods in Reconfigurable. I have also renamed ConfigurationChangeException
to ReconfigurationException and ConfigurationChangeServlet to ReconfigurationServlet to keep
everything consistent.

Please see HDFS-1477 for a patch that makes NameNode Reconfigurable and allows us to change
2 properties.

The servlet now returns error code 500 if a change fails.

A command line tool for changing configuration properties sounds like a good idea but I am
not quite sure how to provide a generic version of such a tool. If the command line tool runs
locally, very little functionality beyond calling the interface methods would be needed. Maybe
it would be best to leave command line utilities to a later JIRA once it becomes more clear
if there is a need for additional support.

> 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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