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https://issues.apache.org/jira/browse/HADOOP-785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12517354
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Arun C Murthy commented on HADOOP-785:
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bq. Currently, hadoop-default.xml is not supposed to be changed by users. Would
you relax this convention in your proposal? There might be a few variables that
I'd like to set for client and server at the same time (eg. namenode address).
Hmm... how about letting both *server* and *client* values for
{{fs.default.name}}'s {{context}} tag to let people know to it can be specified
in both hadoop-server.xml and hadoop-client.xml, and will be used
appropriately? Would that help? I'd rather keep hadoop-default.xml sacrosanct,
though we don't prevent you from editing it even today - thus it serves as a
gold-standard for everyone.
bq. Why don't you want to split up namenode vs. jobtracker and datanode vs.
tasktracker?
I did think about this, and I really don't see what value a
{HDFS|MR}ServerConfiguration and {HDFS|MR}ClientConfiguration will provide,
which is why I didn't take this route... but I'm open to arguments. Just
separation of physical files doesn't seem enough to warrant 4 classes rather
than 2.
bq. This division could be done with xml comments - I don't think it needs to
be so formal as to need a new field.
I agree, yet it's my take that it is better to institutionalise this by adding
another tag, same with the {{context}} tag. Again this depends on whether or
not we can reach a common ground...
> Divide the server and client configurations
> -------------------------------------------
>
> Key: HADOOP-785
> URL: https://issues.apache.org/jira/browse/HADOOP-785
> Project: Hadoop
> Issue Type: Improvement
> Components: conf
> Affects Versions: 0.9.0
> Reporter: Owen O'Malley
> Assignee: Arun C Murthy
> Fix For: 0.15.0
>
>
> The configuration system is easy to misconfigure and I think we need to
> strongly divide the server from client configs.
> An example of the problem was a configuration where the task tracker has a
> hadoop-site.xml that set mapred.reduce.tasks to 1. Therefore, the job tracker
> had the right number of reduces, but the map task thought there was a single
> reduce. This lead to a hard to find diagnose failure.
> Therefore, I propose separating out the configuration types as:
> class Configuration;
> // reads site-default.xml, hadoop-default.xml
> class ServerConf extends Configuration;
> // reads hadoop-server.xml, $super
> class DfsServerConf extends ServerConf;
> // reads dfs-server.xml, $super
> class MapRedServerConf extends ServerConf;
> // reads mapred-server.xml, $super
> class ClientConf extends Configuration;
> // reads hadoop-client.xml, $super
> class JobConf extends ClientConf;
> // reads job.xml, $super
> Note in particular, that nothing corresponds to hadoop-site.xml, which
> overrides both client and server configs. Furthermore, the properties from
> the *-default.xml files should never be saved into the job.xml.
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