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https://issues.apache.org/jira/browse/HADOOP-7001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921493#action_12921493
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Philip Zeyliger commented on HADOOP-7001:
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I might be grumpy, but I think the right way to deal with configuration changes
in a distributed, fault-tolerant system is to just restart the daemon entirely.
We already have to deal with the daemon suddenly crashing and that not
affecting the system too much, so I'm wary of extra complexity of yet another
process. In practice, many configuration variables are loaded at start time
and then stored as statics: stuff like threadpool sizes, for example. Not to
mention that Configuration objects get copied along, so it's hard to make sure
that a configuration change propagates to all possible children.
I'll point out that the namenode and the jobtracker's fair scheduler already
have mechanisms for dynamic configuration changes. In namenode, that's
-refreshNodes. In the jt, I think the fair scheduler re-reads its XML
configuration file on occasion. Both of these make a lot of sense: these are
specific endpoints for managing specific data, and the semantics of those
changes are easy to understand.
-- Philip
> 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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