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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-785) Divide the server and client configurations
Date Wed, 15 Aug 2007 22:17:31 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12520113
] 

Doug Cutting commented on HADOOP-785:
-------------------------------------

It sounds like we're mostly in agreement.  We agree that there should be a file with values
that jobs can override, and that's where most things should go.  There also needs to be a
way for mapreduce daemons to list parameters that may not be overridden by jobs.  Where we
differ is what the files should be named and how the non-overrideable parameters should be
named.  These seems like mostly cosmetic differences that should be easily resolved by reasonable
folks.

I'd prefer it if:

 - The override mechanism is not specific to mapreduce, since other daemons may wish to use
it in the future.  We should also avoid the terms 'client' and 'server', since these are relative,
not universal.

-  The override specification format is merge-friendly, since, e.g., both mapreduce and hdfs
may have values that jobs should not override, and changes to the file should be easy to see
with, e.g., 'diff'.  In other words, different parameters and values should be on different
lines.

Finally, it makes sense to me that the value which cannot be overridden could be set in the
same place where it is declared to be not overrideable.  So, unless we want to invent a new
file format, this sounds a lot like a special config file.

> 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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