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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-785) Divide the server and client configurations
Date Fri, 03 Aug 2007 15:29:53 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12517561
] 

Arun C Murthy commented on HADOOP-785:
--------------------------------------

bq. To summarize, we might end up having a couple of duplicate config items, potentially having
different values. Does this seem like a problem?

Sorry if I wasn't clear before, but this proposal is _explicitly designed_ keeping in mind
tricky knobs such as {ipc.client.connection.maxidletime} and this is how it would work:

One can, and should, specify different values for  {ipc.client.connection.maxidletime} in
hadoop-server.xml and hadoop-client.xml. Now, the values seen by ServerConfiguration (reads
hadoop-default.xml and hadoop-server.xml) viz. used by the {{TaskTracker}} is clearly different
from that seen by the child-vm which uses {{ClientConfiguration}}.

So, yes, in summary this proposal encourages and facilitates the *same* config knobs being
setup separately for use in different contexts...

> 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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